Luminescent lanthanide-doped...
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Department of Inorganic and Physical Chemistry Research group f-element coordination chemistry Luminescent lanthanide-doped nanomaterials Thesis submitted to obtain the degree of Master of Science in Chemistry by Linde MIERMANS Academic year 2011 - 2012 Promoter: prof. dr. Rik Van Deun Supervisor: Anna Kaczmarek
Transcript of Luminescent lanthanide-doped...
Department of Inorganic and Physical Chemistry
Research group f-element coordination chemistry
Luminescent lanthanide-doped nanomaterials
Thesis submitted to obtain
the degree of Master of Science in Chemistry by
Linde MIERMANS
Academic year 2011 - 2012
Promoter: prof. dr. Rik Van Deun
Supervisor: Anna Kaczmarek
Department of Inorganic and Physical Chemistry
Research group f-element coordination chemistry
Luminescent lanthanide-doped nanomaterials
Thesis submitted to obtain
the degree of Master of Science in Chemistry by
Linde MIERMANS
Academic year 2011 - 2012
Promoter: prof. dr. Rik Van Deun
Supervisor: Anna Kaczmarek
Acknowledgements
I would like to thank Prof. Dr. Rik Van Deun for giving me the opportunity to do my thesis in
his research group, for introducing me to the world of lanthanide chemistry and the recently
obtained luminescence set-up.
Special thanks for my supervisor Anna Kaczmarek. I was able to learn a great deal from her.
She was always available whenever I had a question. Not only did she help me scientifically,
but my knowledge of the English language also improved strongly thanks to her. I want to
thank her for correcting and proof reading my thesis, for passing long afternoons at the TEM
with me, but also for the fun moments we had together. I truly think she did a great job as
my supervisor.
I also want to thank Roel Decadt for his extra help with luminescence measurements.
Funding from the Hercules Foundation (project AUGE/09/024 “Advanced Luminescence
Setup”), the Research Foundation Flanders (FWO-Vlaanderen; project G.0081.10N) and
Ghent University (UGent; project BOF 01N01010) is gratefully acknowledged
For the always quickly performed XRD and elemental analysis measurements I would like to
thank Tom Planckaert. I would also like to thank him for answering my technical questions.
I would like to thank my fellow thesis-student Stefanie Smeets for all the fun moments in the
lab, helping out now and then and for keeping me company during long measurements or
when I worked late in the evening. Also the fun times aside school cannot be forgotten. For
support, distraction and help with all kinds of stuff I would also like to thank my classmates of
the University of Hasselt: Geert-Jan Graulus, Frank Driessen and Bart Verbraeken. We had 5
great years.
Finally I want to thank my dad for giving me the chance to go to university and for the
support during those 5 years.
LUMINESCENTE LANTHANIDE-GEDOTEERDE NANOMATERIALEN
L. Miermansa, A. Kaczmarek
a, R. Van Deun
a
a Departement Anorganische en Fysische Chemie, Universiteit Gent, Gent, België
De synthese van lanthaancarbonaat nanopartikels in afwezigheid van
een ligand onder hydrothermale omstandigheden werd onderzocht.
Verschillende lanthaan- en carbonaatbronnen werden gebruikt.
Geselecteerde stalen werden gedoteerd met Tb3+
en Eu3+
. Een
luminescentielevensduur van 1,6 ms voor Tb3+
en 620 μs voor Eu3+
opgenomen in vaste toestand werd gemeten. Er werd geprobeerd
core/shell nanopartikels te synthetiseren met lanthaancarbonaat als
anorganische kern en een organisch ligand als schil. Verschillende
liganden werden hiervoor geselecteerd, maar de pogingen bleken niet
succesvol. Glucose bleek wel een interessant effect te hebben op de
morfologie van de partikels. Core/shell nanopartikels werden verkregen
met een fluoride kern.
Inleiding
Nanopartikels zijn partikels die minstens in één dimensie kleiner zijn dan 100 nm. Door deze
kleine dimensies kunnen de eigenschappen van het materiaal sterk verschillen van deze van
het bulk materiaal. Dit is het gevolg van kwantum-effecten die op deze grootte domineren.
Eigenschappen zoals fluorescentie of elektrische geleidbaarheid kunnen bijvoorbeeld
veranderen. Tegenwoordig wordt er veel onderzoek gedaan naar zulke materialen en vaak
wordt nanotechnologie reeds in hedendaagse commerciële producten gebruikt zoals in
zonnecrèmes, katalysatoren, elektronische apparaten,… [1]
Lanthaniden zijn een speciale groep van elementen in de periodieke tabel. Binnen deze serie
wordt de 4f schil gevuld en deze elementen zijn vooral gekend omwille van hun luminescentie
eigenschappen. Er zijn 3 mogelijke elektronische transities: een ladingstransfer transitie
(LMCT of MLCT), 4f-5d transities en de f-f transities. Het is vooral deze laatste transitie die
de interesse opwekt omwille van zijn unieke aard. De 4f elektronen worden van hun omgeving
afgeschermd door de gevulde 5s en 5p orbitalen. Hierdoor interageren de 4f elektronen slechts
zwak met hun omgeving en wordt de structuur van de energieniveaus van het vrije ion
behouden in vrijwel elke chemische matrix. Hierdoor zijn de signalen in optische spectra
scherp en makkelijk herkenbaar. [2, 3] Ongelukkigerwijze zijn deze 4f-transities verboden
door de Laporte selectieregel. Lage molaire absorptiecoëfficiënten en een lange
luminescentielevensduur zijn hier het gevolg van. Deze langlevende geëxciteerde toestand kan
gemakkelijk gequenched worden door hoge energie vibraties van organische functionele
groepen zoals OH-groepen. Dit reduceert mogelijke toepassingen in een organische omgeving.
[2, 4] De molaire absorptiecoëfficiënt kan verhoogd worden door gebruik te maken van het
antenne-effect. Het ligand gebonden aan het Ln3+
-ion wordt geëxciteerd en zal zijn energie
doorgeven aan het Ln3+
-ion waardoor dit op zijn beurt geëxciteerd wordt. Vervolgens kan het
Ln3+
-ion relaxeren via luminescentie. [2, 3]
Er zijn reeds verschillende publicaties over lanthanide nanopartikels verschenen [5-12], maar
slechts enkele over lanthanidecarbonaat nanopartikels. Dysprosiumcarbonaat nanopartikels
werden gesynthetiseerd via sonochemische synthese. Deze partikels dienden als precursor
voor de synthese van dysprosiumoxide nanopartikels. [13] Gadoliniumcarbonaat partikels
gedoteerd met Eu3+
werden gesynthetiseerd met behulp van ureum. De invloed van de
reactietijd werd onderzocht. Na calcinatie werden Gd2O3 nanopartikels verkegen. [14]
Lanthaancarbonaat nanodraden werden verkregen via een synthese gebruik makend van een
‘geïnverteerd micellen systeem. Verschillende reactieparameters zoals pH, reactietijd en
reactietemperatuur werden onderzocht. [15] Lanthaancarbonaat nanopartikels werden
verkregen via sonochemische synthese. Deze partikels werden gebruikt als precursor voor de
synthese van lanthaanhydroxide en lanthaanoxide nanopartikels. [16]
Core/shell nanopartikels zijn nanostructuren bestaande uit een kern en een schil gemaakt van
twee verschillende materialen. Hun dimensies liggen meestal tussen de 20 en 200 nm. Door de
juiste schil te kiezen kunnen de eigenschappen van de core/shell nanopartikels verbeterd
worden ten op zichtte van de ‘gewone’ nanopartikels. Verbetering in monodispersiteit,
oplosbaarheid, stabiliteit (thermisch of chemisch),... is mogelijk. Er zijn verschillende
mogelijkheden in het kiezen van de core/shell structuur maar in deze thesis zal er gewerkt
worden met een anorganische kern en een organische schil. [17] Luminescerende Ln3+
-ionen
kunnen dan gedoteerd worden in het anorganische deel van de partikels waardoor ze
beschermd worden tegen de (organische) omgeving. Afhankelijk van het gekozen ligand
gebruikt voor de organische schil zijn de partikels oplosbaar in organische solventen of water.
[4, 18] Water gebaseerde systemen hebben verschillende voordelen: deze systemen zijn
milieuvriendelijker, de synthese is eenvoudig, veilig en er zijn geen speciale atmosferische
condities nodig, verder is er ook een groter potentieel voor bulk productie. [19] Een van de
meest gebruikte liganden voor water oplosbare core/shell nanopartikels is citroenzuur. [3, 19-
25] Lanthanidefluoride materialen voor de kern zijn erg populair. Deze materialen hebben een
lage vibrationele energie waardoor de quenching van de Ln3+
-ionen minimaal is. [26] Van
Veggel et al. heeft al veel onderzoek verricht in het gebied van water oplosbare core/shell
lanthanide nanopartikels. Als kernmateriaal wordt meestal LaF3 gebruikt. De organische schil
is vaak citroenzuur, [3, 20, 23, 24] maar ook andere liganden worden gebruikt. [23, 24, 27]
LaF3 als kernmateriaal werd ook door andere onderzoeksgroepen gekozen. Als schil werden
verschillende liganden gebruikt. [26, 28-31] Yb3+
-Er3+
gedoteerde LaF3 nanokristallen gecoat
met glucose werden gesynthetiseerd door Shan et al. De partikels hadden een rechthoekige
vorm en een grootte tussen 15-20 nm. De invloed van de pH werd onderzocht en upconversion
spectra werden opgenomen. [30] Ook andere (fluoride gebaseerde) anorganische materialen
werden reeds gebruikt als kern. [19, 21-25, 32-38] LnVO4 (Ln= Y, Dy, Er, Ce, Gd) werden
gesynthetiseerd door gebruikt te maken van natriumcitraat, natriumtartraat, natriummalaat. De
morfologie van de partikels bleek afhankelijk van het gebruikte ligand. [38] 2-aminoethyl
fosfaat (AEP) werd gebruikt om verschillende LnF3 materialen te coaten, zowel gedoteerd als
niet gedoteerd. [23, 24, 28] Zelfs liganduitwisseling met 6-carboxy-5’-methyl-2,2’-bipyridine
bleek mogelijk te zijn waardoor de luminescentie verbeterd werd ten op zichtte van de AEP-
gestabiliseerde partikels. [28] Ook bioconjugatie bleek mogelijk te zijn uitgaande van
nanopartikels gecoat met AEP. [39]
Waarschijnlijk een van de meest belangrijke toepassingen voor dit soort core/shell
nanopartikels is het labelen van biomoleculen met een luminescerend label. Conventionele
fluorescente labels hebben hun voordelen zoals kleine grootte, erg water oplosbaar,
gemakkelijk te gebruiken en bestaande standaardprocedures voor hun bioconjugatie. Toch
hebben deze ook nadelen zoals een breed spectrum en lage fotochemische stabiliteit. Ln3+
-
gedoteerde water oplosbare core/shell nanopartikels zijn een veelbelovende oplossing. Indien
juist gekozen, kan het organische ligand bioconjugatie vergemakkelijken. Bovendien is het
emissiespectrum van zo’n partikel gekarakteriseerd door smalle pieken. De optische
eigenschappen worden bepaald door de Ln3+
-ionen gebruikt om te doteren. De partikels zijn
fotochemisch stabiel, hebben een grote Stokes shift en een lange luminescentie levensduur. Er
zijn al verschillende voorbeelden gekend waarbij bioconjugatie mogelijk bleek te zijn. [18, 31,
39-41]
Het doel van dit project was om lanthaancarbonaat core/shell nanopartikels te synthetiseren.
Als ligand werd glucose, appelzuur en 2-aminoethyl fosfaat gekozen. Ook ongecoate
lanthaancarbonaat nanopartikels werden gesynthetiseerd. Deze werden ook gedoteerd met
Eu3+
en Tb3+
, welke beide emitteren in het zichtbare gebied. De syntheses waren water
gebaseerd.
Materialen en methodes
De gebruikte chemicaliën zijn: lanthaannitraat (La(NO3)3•6 H2O) 99,99% gekocht bij Roth,
ureum (CH4N2O) pro analyse, rokend zoutzuur 37% voor analyse (HCl) verkregen via Merck,
watervrij α-D-glucose (C6H12O6), appelzuur (C4H6O5) 99%, 2-aminoethyl fosfaat (AEP),
natriumfluoride (NaF) 99%, lanthaanacetaat (La(OAc)3•6 H2O) 99,99%, yttriumnitraat
(Y(NO3)3·6 H2O) 99,99% en ammoniakoplossing (NH3(aq)) 30% gekocht bij Sigma Aldrich.
Watervrij natriumcarbonaat (Na2CO3) werd verkregen via UCB. Methanol (MeOH) en ethanol
(EtOH) AnalaR NORMAPUR werden gekocht bij VWR. Natriumhydroxide 98% (NaOH)
verkregen via Chemlab. Alle chemicaliën werden gebruikt zonder verdere zuivering.
Infrarood metingen werden gedaan met behulp van een Thermo Scientific FT-IR spectrometer
(type Nicolet 6700) uitgerust met een DRIFTS-cel. KBr werd gebruikt als achtergrond. Het
spectrum wordt opgenomen van 700 cm-1
tot 4000 cm-1
met een resolutie van 4 cm-1
Voor TEM metingen werd een JOEL JEM2200FS transmissie elektronen microscoop gebruikt
met een versnellingsvoltage van 200 kV. De beelden werden verkregen op een Gatan CCD
camera. Als staalvoorbereiding werden de stalen opgelost in water en werd een druppel van
deze oplossing geplaatst op een koperen grid (200 mesh, bedekt met een koolstoffilm) zodat
het solvent kon verdampen.
Poeder-XRD werd uitgevoerd op een Thermo Scientific ARL X’TRA diffractometer uitgerust
met een Cu Kα (λ = 1.5405 Å) bron, een goniometer en een Peltier gekoelde Si(Li) solid state
detector. De stalen werden fijngemalen voor de meting.
Element analyse werd gedaan via verbrandingsanalyse (CHN-analyse). Een Thermo
Scientific* FLASH 2000 Series CHNS/O Analyzer werd gebruikt. Detectie gebeurde via
thermische geleidbaarheid.
Luminescentie spectra werden opgenomen met een Double Edinburgh Instruments FLSP920 /
FSP920 spectrometer setup. Enkel systeem 1, een UV-vis-NIR spectrometer werd gebruikt.
Een 450W xenon lamp als steady state excitatie bron, werd gebruikt. Emissiespectra en
levensduur werd gemeten zowel in suspensie (0,01 g poeder in 2 ml water) als in poeder vorm.
De Tb3+
emissiespectra werden opgenomen bij een excitatie golflengte van 351 nm van 450
nm tot 650 nm. De stapgrootte was 0,5 nm, de dwell time 0,5 s. Voor de suspensies werd de
scan slit op 0,5 nm en de fixed slit op 5 nm ingesteld. Voor de vaste stalen was de scan slit 0,5
nm en de fixed slit 0,2 nm.
De Eu3+
emissiespectra werden opgenomen bij een excitatie golflengte van 395 nm van 550
nm tot 750 nm. Andere parameters werden gelijk gehouden. Voor de suspensies was de scan
slit ingesteld op 0,3 nm en de fixed slit op 5 nm. Voor de vaste stalen was de scan slit 0,3 nm
en de fixed slit 0,7 nm.
Synthese
Lanthaancarbonaat nanopartikels
Een hydrothermale synthese met variërende condities werd uitgevoerd. Zowel Na2CO3 als
ureum werden als carbonaatbron gebruikt. Als lanthaanbron werd La(NO3)3 of La(OAc)3
gebruikt. Als reactietemperatuur werd 120 of 140 °C gekozen. De reactietijd bedroeg 12 of 24
uur. De exacte reactieparameters van geselecteerde reacties zijn samengevat in tabel 1. Na de
reactie werd een wit poeder verkregen wat gewassen werd met MeOH of EtOH en gedroogd
in de oven (60 °C). De partikels verkregen via synthesecondities ZL 18 werden gedoteerd met
variërende percentages (2%-20%) Tb3+
en Eu3+
.
TABEL I.
Staal Hoeveelheid
La(NO3)3 (mmol)
Hoeveelheid
La(OAc)3 (mmol)
Hoeveelheid
ureum (mmol)
Hoeveelheid
water (ml)
Tijd
(u)
Reactie
temperatuur
(°C)
ZL
18
1,5 - 15 20 24 120
ZL
19
- 1,5 15 20 24 120
ZL
28
1,5 - 15 50 12 140
Lanthaancarbonaat nanopartikels in de aanwezigheid van een ligand
Verschillende liganden werden geselecteerd om core/shell nanopartikels te synthetiseren. Alle
reacties waren fles-reacties. De algemene reactieparameters zijn samengevat in tabel 2. Alle
componenten werden apart opgelost. De oplossing die het ligand bevatte werd geneutraliseerd
indien nodig met een waterige NH3-oplossing. Aan deze oplossing werd de lanthanide-
oplossing toegevoegd. Als laatste werd de carbonaatbron toegevoegd. In het geval van AEP en
appelzuur werden de producten geprecipiteerd en gewassen met MeOH of EtOH alvorens te
drogen. In het geval van glucose werden de partikels gezuiverd door verschillende cycli van
precipiteren met behulp van een NaOH-oplossing en heroplossen met behulp van een HCl-
oplossing uit te voeren.
TABEL II.
Ligand Hoeveelheid
La(NO3)3 (mmol)
Hoeveelheid
ligand (mmol)
Hoeveelheid
ureum/Na2CO3
(mmol)
Hoeveelheid
water (ml)
Tijd
(u)
Reactie
temperatuur
(°C)
AEP 1,5 4 15/1,5 30 2/3 85
Appelzuur 1,5 4/8 15/- 50 3 80
Glucose 1,5 4/8/12 15/- 50 3 85
Fluoride core/shell nanopartikels
De synthese volgens Shan et al.[30] werd gemodificeerd. 2 g glucose werd opgelost in 20 ml
water en 0,156 g NaF werd toegevoegd terwijl de oplossing geroerd werd. Het reactiemengsel
werd verwarmd tot 60 °C waarna 0,65720 g La(NO3)3 opgelost in 3 ml water werd
toegevoegd. De reactietijd bedroeg 1,5 uur (Gluc 6) of 3 uur (Gluc 17). Na de reactie werd een
heldere suspensie verkregen. De partikels werden geprecipiteerd met behulp van een NaOH-
oplossing en heropgelost met behulp van een HCl-oplossing. Dit werd verschillende keren
herhaald om zo het product te zuiveren. De verkregen producten werden gedroogd in de oven
(60 °C). Reactie Gluc 6 werd ook herhaald met Y(NO3)3 (Gluc 15) als lanthanide bron. Een
Witte suspensie werd verkregen. Deze werd gewassen met EtOH of MeOH alvorens te
drogen.
Resultaten en bespreking
Lanthaancarbonaat nanopartikels
De verkregen poeders werden getest voor hun oplosbaarheid in water. Geen van de verkregen
poeders was oplosbaar in water. Onstabiele suspensies werden verkregen.
XRD metingen toonden aan dat voornamelijk LaOHCO3 in de hexagonale fase gevormd werd.
In sommige gevallen werd een mengsel van de hexagonale en orthorhombische fase gevormd
(ZL 28). Dit leek willekeurig en geen precieze verklaring werd hiervoor gevonden. Voor
zowel ZL 18 als ZL 19 werd de hexagonale fase gevormd (figuur 1). Elementanalyse toont aan
dat er bijna geen N wordt ingebouwd wat eventueel afkomstig kan zijn van het gebruikte
ureum.
Figuur 1. XRD spectra van de hydrothermaal gesynthetiseerde partikels
De grootte en morfologie van de verkregen partikels werd bestuurd met behulp van TEM-
metingen. Wanneer La(NO3)3 als lanthaanbron gebruikt word tezamen met Na2CO3 als
carbonaatbron zijn de partikels zeer groot en geaggregeerd. Er wordt geschat dat de partikels
tussen de 400 en 1000 nm zijn. Ureum als carbonaatbron geeft betere resultaten, maar noch
verdunning, temperatuur of tijd lijken een specifieke invloed te hebben. De beste resultaten
werden verkregen voor ZL 18 (figuur 2). De partikels zijn nog steeds redelijk groot (minstens
100 nm), maar minder geaggregeerd dan het geval was met Na2CO3 als carbonaatbron.
Opvallend betere resultaten worden verkregen wanneer La(OAc)3 wordt gebruikt als
lanthaanbron (figuur 2). Zowel met ureum als Na2CO3 als carbonaatbron zijn de verkregen
partikels klein, maar hebben ze een brede grootteverdeling (20-60 nm). In het geval van
Na2CO3 zijn de partikels wel sterk geaggregeerd.
Figuur 2. TEM afbeeldingen van ZL 18 (La(NO3)3 en ureum ) en ZL 19 (La(OAc)3 en ureum)
De partikels verkregen met behulp van synthese ZL 18 werden gedoteerd met Tb3+
en Eu3+
.
Doteren met Tb3+
bleek de gevormde fase te veranderen. Een duidelijke piek kon gezien
worden op 20 graden en enkele additionele pieken tussen 30 en 40 graden konden
onderscheiden worden. Het XRD spectrum kwam sterk overeen met de XRD spectra van de
partikels in gemengde fase. Mogelijk heeft Tb3+
op een of andere manier invloed heeft op de
gevormde fase. (zie figuur 1, ZL 51) In het geval van doteren met Eu3+
werden geen
veranderingen in fase vastgesteld (zie figuur 1, ZL 59).
De emissiespectra werden zowel in suspensie als in vaste vorm opgenomen en waren zeer
vergelijkbaar. Het emissiespectrum van de partikels in vaste fase gedoteerd met 10% Tb3+
(ZL
51) is weergeven in figuur 3. De 5D4→
7F6 transitie is te zien bij 490 nm, de
5D4→
7F5,
5D4→
7F4 and
5D4→
7F3 transities vinden plaats bij 540 nm, 580 nm en 620 nm respectievelijk.
De intensiteiten van de emissiespectra stijgen tot een dotteringspercentage van 10% waarna ze
afnemen. Dit is waarschijnlijk ten gevolge van zelf-quenching. De levensduur was iets hoger
in vaste fase (1,7 ms) dan in suspensie (1,6 ms). Er werd slechts een lichte daling verwacht
aangezien de luminescerende Ln3+
-ionen ingebed zitten in de anorganische matrix en
afgeschermd zouden moeten zijn van de waterige omgeving, welke een sterk quenchend effect
heeft. Enkel de Ln3+
- ionen aan het oppervlak worden gequenched. De lichte stijging wat
betreft levensduur in de vaste fase is het gevolg van de Ln3+
-ionen aan het oppervlak die nu
niet meer gequenched worden.
Het emissiespectrum van de partikels in vaste fase gedoteerd met 15% Eu3+
(ZL 59) is
weergeven in figuur 3. Bij 580 nm kan de 5D0→
7F0 transitie waargenomen worden en bij 590
nm is de 5D0→
7F1 transitie zichtbaar. Drie pieken kunnen onderscheiden worden. Deze grote
opsplitsing is het gevolg de lage symmetrie van de verbinding. Bij 617 nm is de 5D0→
7F2
transitie te zien. Deze piek is vrij intens wat opnieuw een indicatie is voor lage symmetrie. De 5D0→
7F3 en
5D0→
7F4 transities zijn te zien bij 652 nm en 690 nm. Een levensduur van 620-
650 μs werd verkregen in vaste toestand, in suspensie lag deze iets lager (600 μs).
Figuur 3. Emissie spectra in de vaste fase van ZL 51 (Tb3+) en ZL 59 (Eu3+)
Lanthaancarbonaat nanopartikels in de aanwezigheid van een ligand
Verschillende liganden werden gebruikt met het oog op de synthese van core/shell
nanopartikels. In geen van de gevallen werden core/shell nanopartikels gevormd.
In het geval van AEP werd na synthese een heldere oplossing verkregen. XRD toonde echter
aan dat de gevormde producten amorf waren. De verkregen producten waren water-oplosbaar,
maar het Tyndall effect kon niet geobserveerd worden. Er werden geen partikels gezien bij
TEM metingen. DRIFT metingen noch elementanalyse kon uitsluitsel geven over de precieze
aard van het gevormde product. Vermoedelijk wordt er een water-oplosbaar complex
gevormd. Waarschijnlijk is AEP als ligand te sterk waardoor de carbonaationen niet kunnen
concurreren met AEP en bijgevolg ook niet binden aan het lanthanide-ion. De reactie werd
ook uitgevoerd in afwezigheid van carbonaatbron. Elementanalyse toonde aan dat er geen
significant verschil is in de hoeveelheid koolstof aanwezig in het product. In afwezigheid van
carbonaatbron werd echter geen water-oplosbaar product verkregen en ook XRD en DRIFT
metingen geven aan dat het gevormde product mogelijk verschilt.
Voor appelzuur werden water-oplosbare producten verkregen bij het gebruik van 8 mmol
appelzuur (zie ook tabel 2). Ook in dit geval was het Tyndall effect niet te zien. In alle andere
gevallen vormde de verkregen poeders een suspensie waarvan de stabiliteit vergelijkbaar was
met de eerder verkregen LaOHCO3 nanopartikels. XRD metingen gaven opnieuw aan dat alle
verkregen poeders amorf zijn. De reacties waarbij 8 mmol appelzuur en 4 mmol appelzuur
werden gebruikt werden herhaald zonder carbonaatbron. Elementanalyse toont aan dat er
amper extra koolstof wordt ingebouwd bij het gebruik van een carbonaatbron wanneer 8 mmol
appelzuur gebruikt wordt. Er werden geen partikels gevisualiseerd bij TEM-metingen.
Waarschijnlijk is ook in dit geval het ligand te sterk en wordt er een water-oplosbaar complex
gevormd. Indien slechts 4 mmol appelzuur gebruikt wordt toont elementanalyse wel aan dat er
een kleine hoeveelheid extra koolstof wordt ingebouwd indien een carbonaatbron gebruikt
wordt. TEM metingen tonen aan dat partikels gevormd worden, maar deze zijn erg groot en
geaggregeerd. Er is nu minder ligand aanwezig waardoor er minder competitie is tussen de
carbonaat-ionen en het ligand. Dit zou als gevolg kunnen hebben dat er kleine hoeveelheden
(amorf) lanthaancarbonaat gevormd worden. Appelzuur lijkt echter te klein als ligand om de
grootte of morfologie van de partikels te beïnvloeden.
In het geval van glucose (zie ook tabel 2) werden water-oplosbare producten verkregen indien
12 mmol glucose gebruikt werd en alvorens de producten te drogen. Het Tyndall effect was
niet zichtbaar. Indien de poeders gedroogd werden, waren deze niet meer water-oplosbaar.
TEM metingen van de producten voor de droogfase tonen aan dat er partikels aanwezig zijn,
maar deze zijn niet uniform in grootte. De partikels zijn een mengsel van staafvormige en
kubusvormige partikels. De XRD van het poeder vertoonde enkele scherpe pieken, maar deze
konden niet geïdentificeerd worden. Er moet wel rekening mee gehouden worden dat de XRD
werd opgenomen na drogen en er mogelijk decompositie kon optreden. Ook DRIFTS
metingen konden geen uitsluitsel geven over de precieze samenstelling van de partikels.
Vermoedelijk worden de partikels enkel als bijproduct gevormd, in kleine hoeveelheden. Dit
kan mogelijk het waarnemen van het Tyndall effect verstoren. Wanneer er slechts 4 of 8 mmol
glucose gebruikt worden veranderen de resultaten significant. De verkregen poeders zijn niet
langer water-oplosbaar maar vormen onstabiele suspensies. XRD toont aan dat
La2O(CO3)2·1,4 H2O gevormd wordt. TEM metingen tonen aan dat er lange staafvormige
partikels van ongeveer 200 nm in diameter gevormd worden (figuur 4). Hoe hoger de
gebruikte hoeveelheid glucose, hoe sterker de partikels aggregeren.
Figuur 4. TEM beeld van de gevormde La2O(CO3)2·1,4 H2O partikels
Fluoride core/shell nanopartikels
De poeders verkregen via Gluc 6 en Gluc 17 waren resuspendeerbaar in water. Het Tyndall
effect was te zien. XRD metingen toonde aan dat LaF3 was gevormd. In beide gevallen
werden kleine, geaggregeerde partikels (± 10 nm) gevisualiseerd onder de TEM (figuur 5).
Wanneer La(NO3)3 vervangen werd door Y(NO3)3 als lanthanide bron werd YF3 gevormd.
Een witte, maar vrij stabiele suspensies werd verkregen wanneer het poeder geresuspendeerd
werd in water. Staafvorminge partikels bestaande uit individuele draden werden gevormd
(figuur 5)
Figuur 5. TEM beeld van Gluc 17 (links) en Gluc 15 (rechts)
Conclusie
Het initiële doel van het project, de synthese van core/shell nanopartikels met
lanthaancarbonaat als anorganische kern, werd niet gehaald. Verschillende liganden werden
getest, maar het bleek niet mogelijk core/shell nanopartikels te synthetiseren. Men kan
concluderen dat lanthaancarbonaat waarschijnlijk niet geschikt is als kernmateriaal. Wel werd
geobserveerd hoe glucose de morfologie en vorm van de lanthaancarbonaat partikels kan
beïnvloeden.
Bevredigende resultaten werden verkregen in de synthese van ongecoatte lanthaancarbonaat
nanopartikels. Kleine partikels werden verkregen met La(OAc)3 als lanthaanbron. De synthese
condities van ZL 18 werden geselecteerd om Eu3+
en Tb3+
gedoteerde nanopartikels te maken.
Een luminescentelevensduur van 1,6 ms voor Tb3+
en 600 μs voor Eu3+
in vaste toestand
werden verkregen.
Core/shell partikels werden verkregen wanneer er gewerkt werd met een fluoride kern.
Veranderen van lanthanidebron leverde interessante morfologische veranderingen op.
Dankwoord
Ik zou graag prof. Dr. Rik Van Deun bedanken om mij de kans te geven om een thesis in zijn
onderzoeksgroep te doen. Mijn begeleidster Anna Kaczmarek wil ik bedanken voor alle hulp
gedurende het hele jaar, voor het verbeteren van mijn thesis en voor alle TEM metingen. Tom
Plankaert zou ik graag bedanken voor het uitvoeren van XRD metingen en element analyses. Financiële steun van de Hercules stichting (project AUGE/09/024 “Advanced Luminescence
Setup”), het FWO-Vlaanderen (project G.0081.10N) en de Universiteit Gent (BOF-project
01N01010) is in dank aanvaard.
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23. Evanics, F., et al., Water-Soluble GdF3 and GdF3/LaF3 NanoparticlesPhysical Characterization and NMR Relaxation Properties. Chemistry of Materials, 2006. 18(10): p. 2499-2505.
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25. Huignard, A., et al., Synthesis and Characterizations of YVO4:Eu Colloids. Chemistry of Materials, 2002. 14(5): p. 2264-2269.
26. Wei, Y., et al., Polyol-mediated synthesis of water-soluble LaF3:Yb,Er upconversion fluorescent nanocrystals. Materials Letters, 2007. 61(6): p. 1337-1340.
27. Diamente, P. and F. Veggel, Water-Soluble Ln+3-Doped LaF3 Nanoparticles: Retention of Strong Luminescence and Potential as Biolabels. Journal of Fluorescence, 2005. 15(4): p. 543-551.
28. Charbonniere, L.J., et al., Highly luminescent water-soluble lanthanide nanoparticles through surface coating sensitization. New Journal of Chemistry, 2008. 32(6): p. 1055-1059.
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30. Shan, G., et al., A simple, low-temperature route to synthesize aqueous-dispersible Yb3+–Er3+ co-doped hexagonal LaF3 nano-crystals for up-conversion fluorescence. Materials Letters, 2008. 62(26): p. 4187-4190.
31. Wang F, Z.Y., Fan XP, Wang MQ, One-pot synthesis of chitosan/LaF3/Eu+3 nanocrystals for bioapplications. Nanotechnology, 2006. 17: p. 1527-1532.
32. Wang, L., Y. Zhang, and Y. Zhu, One-pot synthesis and strong near-infrared upconversion luminescence of poly(acrylic acid)-functionalized YF<sub>3</sub>:Yb<sup>3+</sup>/Er<sup>3+</sup> nanocrystals. Nano Research, 2010. 3(5): p. 317-325.
33. Wang, M., et al., One-step synthesis and characterization of water-soluble NaYF4:Yb,Er/Polymer nanoparticles with efficient up-conversion fluorescence. Journal of Alloys and Compounds, 2009. 485(1–2): p. L24-L27.
34. Chen, H., et al., Water-soluble Yb3+, Tm3+ codoped NaYF4 nanoparticles: Synthesis, characteristics and bioimaging. Journal of Alloys and Compounds, 2012. 511(1): p. 70-73.
35. Wang, F. and X. Liu, Upconversion Multicolor Fine-Tuning: Visible to Near-Infrared Emission from Lanthanide-Doped NaYF4 Nanoparticles. Journal of the American Chemical Society, 2008. 130(17): p. 5642-5643.
36. Wang, F., X. Xue, and X. Liu, Multicolor Tuning of (Ln, P)-Doped YVO4 Nanoparticles by Single-Wavelength Excitation. Angewandte Chemie International Edition, 2008. 47(5): p. 906-909.
37. Huignard, A., T. Gacoin, and J.-P. Boilot, Synthesis and Luminescence Properties of Colloidal YVO4:Eu Phosphors. Chemistry of Materials, 2000. 12(4): p. 1090-1094.
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17
Contents
CONTENTS ........................................................................................................................................ 17
1 INTRODUCTION ........................................................................................................................... 19
2 LANTHANIDES AND CORE/SHELL NANOPARTICLES ....................................................................... 21
2.1 LANTHANIDE NANOPARTICLES.......................................................................................................... 22
2.2 CORE/SHELL NANOPARTICLES .......................................................................................................... 27
2.3 POSSIBLE APPLICATION OF WATER SOLUBLE CORE/SHELL NANOPARTICLES ................................................... 32
3 EQUIPMENT AND USED CHEMICALS ............................................................................................ 35
3.1 DIFFUSE REFLECTANCE INFRARED FOURIER TRANSFORM SPECTROSCOPY (DRIFTS) ....................................... 35
3.2 TRANSMISSION ELECTRON MICROSCOPY (TEM) ................................................................................... 36
3.3 SCANNING ELECTRON MICROSCOPY (SEM) ......................................................................................... 36
3.4 X-RAY DIFFRACTION (XRD) ............................................................................................................. 37
3.5 ELEMENTAL ANALYSIS (EA) ............................................................................................................. 37
3.6 ADVANCED LUMINESCENCE SET-UP ................................................................................................... 38
4 UNCOATED LANTHANUM CARBONATE PARTICLES ....................................................................... 40
5 SYNTHESIS OF LANTHANUM CARBONATE PARTICLES IN PRESENCE OF 2-AMINOETHYL
PHOSPHATE (AEP)............................................................................................................................. 56
6 SYNTHESIS OF LANTHANUM CARBONATE PARTICLES IN PRESENCE OF MALIC ACID (MA) .............. 61
7 SYNTHESIS OF LANTHANUM CARBONATE PARTICLES IN PRESENCE OF GLUCOSE (GLUC) ............... 65
8 LNF3/GLUCOSE CORE/SHELL NANOPARTICLES .............................................................................. 70
9 GENERAL CONCLUSION ............................................................................................................... 75
18
10 REFERENCES ............................................................................................................................. 76
11 APPENDIX ................................................................................................................................. 80
11.1 SYNTHESIS METHODS .................................................................................................................. 80
11.1.1 SYNTHESIS OF LANTHANUM CARBONATE NANOPARTICLES ......................................................................... 80
11.1.2 GLUCOSE COATED FLUORIDE NANOPARTICLES ......................................................................................... 85
11.2 LUMINESCENCE SPECTRA .............................................................................................................. 87
19
1 Introduction
Particles that have at least one dimension less than 100 nm are called nanoparticles.
Properties of a material at such a small size change significantly compared to those larger in
size. This is due to the fact that quantum-effects take over. Quite often properties are size-
dependent and characteristics such as melting point, fluorescence, electrical conductivity,
magnetic permeability, and chemical reactivity can change as a function of the size. A well-
known example is nanoparticles of gold. Normally gold is known by the yellow color, but at
nanoscale it appears red or purple. This can be explained by the fact that at nanoscale the
movement of the gold’s electrons are limited and the nanoparticles react different with light
compared to larger particles. This size-dependence gives rise to the concept of fine-tuning.
By changing the size of the particles one can change the property of interest (for example
changing fluorescence color). Nanoscale materials also have a high surface to volume ratio.
This gives better mass transfer and heat transfer properties as well as higher reactivity.
Materials that have one dimension in the nanoscale (but are larger in the other two
dimensions) are called layers. Thin films and surface coatings are examples of such layers.
Sometimes they are also referred to as nanoplates because they have a thickness at the
nanoscale, but their other two dimensions can be larger. Nanowires and nanotubes have two
dimensions at nanoscale. A nanowire’s/nanotube’s length can be several hundred
nanometers (or longer), but their diameter is within the nanoscale. A nanotube is
comparable with a nanowire, but it is hollow. Nanoparticles are bits of material which have
all three dimensions in the nanoscale.
Nowadays nanotechnology is used in many commercial products and processes. It is used to
manufacture lightweight, strong materials for different applications like boat hulls, sporting
equipment and automotive parts. Furthermore they are used in cosmetics like sunscreens
(nanosized titanium dioxide and zinc oxide). Nanostructured catalysts are known and make
chemical manufacturing processes more efficient by saving energy and reducing waste. There
are examples of nanomaterials used in healthcare. Some nanoceramics are used in specific
dental implants or to fill holes in diseased bones, because their mechanical and chemical
properties can be ‘tuned’ to attract bone cells from the surrounding tissue to make new
20
bone. Almost all high-performance electronic devices manufactured in the past decade are
based on some nanomaterials. [1]
The aim of this project was to synthesize and characterize Ln3+ doped lanthanum carbonate
nanoparticles of the core/shell type where the shell is an organic ligand. The chosen ligands
were glucose, malic acid and 2-aminoethyl phosphate. The synthesis was carried out in a
water-based environment. Using environmentally friendly synthesis has gained importance in
the last years. It offers several advantages such as easier purification of the products, more
convenient bioconjugation with DNA, enzymes etc. and others. Uncoated lanthanum
carbonate particles were synthesized too. To date, no reports of core/shell nanoparticles
with lanthanum carbonate as an inorganic core have been published and only a few reports
about lanthanum carbonate nanoparticles are known. The uncoated particles were doped
with highly luminescent Eu3+ or Tb3+. Both ions emit in the visible region. Eu3+ emits in the red
region (570-720 nm) and Tb3+ emits in the green region (480-680 nm).
21
2 Lanthanides and core/shell nanoparticles
Lanthanides are a special group of elements within the periodic table. In the lanthanide
series the 4f orbitals are being filled. Usually these elements exist as trivalent cations with an
electronic configuration of 4fn, with n varying from 1 (Ce3+) to 14 (Lu3+). There are three types
of electronic transitions possible. The first type is a charge transfer transition. This can be a
ligand to metal (LMCT) as well as a metal to ligand (MLCT) transition. These rather broad
transitions are allowed by Laporte’s selection rule, and they usually appear in the UV region.
Secondly there are the 4f-5d transitions. A 4f electron gets promoted into the 5d sub-shell.
These transitions are allowed, but their energy depends on the metal environment due to
the fact that the 5d orbitals are directly in contact with ligand orbitals or other surroundings.
[2] Finally there are the f-f transitions. In this case the 4f electrons rearrange. These
transitions have a unique nature because the 4f electrons are shielded from the environment
by the filled 5s and 5p orbitals so the 4f electrons only interact weakly with the chemical
environment. The free ion energy-level structure of Ln3+-ions is therefore largely preserved in
any chemical matrix and the Crystal Field theory for example can be considered as a
perturbation. The optical spectra are dominated by sharp-line structures and quite easily
recognizable. [2, 3] Unfortunately these 4f-transitions are forbidden by Laporte’s selection
rule and low molar absorption coefficients (< 10 M-1 cm-1 or even < 1 M-1 cm-1) as well as long
luminescence lifetimes are the consequence. Most Ln3+-ions are luminescent. Only La3+ and
Lu3+ have no f-f transitions and do not show luminesce. The emission of the ions covers the
entire spectrum from UV until NIR. [2, 4] Yet the long-living excited state can be quenched
quite easily by the high-energy vibrations of organic solvents, polymers or ligands. This
reduces application possibilities in an organic environment. [4] The low molar absorption
coefficients can be circumvented by using a sensitizer. Usually one uses ligands bonded to
the Ln3+-ion. One must take care that the ligand absorbs strongly the used excitation
wavelength. Due to this the ligand gets excited. The ligand should transfer its energy to the
lanthanide ion. This is the ‘antenna-effect’ and it increases the molar extinction coefficient.
[2, 3] Another interesting property of several lanthanide ions is upconversion (UC). This is a
process in which two NIR photons are converted into one visible photon. Ho3+, Pr3+, Nd3+,
22
Yb3+ are some examples of ions that can be used for upconverting processes.
Downconversion (DC) or quantum-cutting (QC) implies splitting one energetic photon (UV or
visible) into two lower energy photons. The process requires a pair of ions. Ions usable for DC
are for example Eu3+, Tb3+, Er3+, Gd3+. Concerning photoluminescence the overall efficiency is
an important parameter and can be approximated by the following equitation:
with the overall quantum yield and the molar absorptivity at the excitation
wavelength. Using sensitization through the ligand levels the overall quantum yield can be
described by
is the intrinsic quantum yield, represents the efficiency with which electromagnetic
energy is transferred from the surroundings onto the metal ion, is the experimental
lifetime of the metal excited state (measured upon direct excitation) and stands for the
radiative lifetime. depends on the energy gap between the lowest excited (emissive)
state and the highest level of its ground multiplet. The smaller this gap, the easier non-
radiative deactivation processes occur. [2]
2.1 Lanthanide nanoparticles
There are several reports on lanthanide nanoparticles. Gadolinium nanoparticles were
synthesized by alkalide reduction. The nanoparticles ignited spontaneously upon exposure to
air allowing Gd2O3 to form. [5] Nanoparticles consisting of lanthanide oxides have also been
reported. Hollow spheres of lutetium oxide were synthesized by a template-directed route.
Carbon spheres were used as a template. The wall thickness was about 40 nm. The hollow
spheres were doped with Eu3+ and Er3+. [6] Y2O3:Eu3+ nanoparticles were prepared using urea
in a non-aqueous solution. The particles were spherical but quite large and with a broad size
distribution, however the photoluminescence was enhanced. [7] Erbium oxide nanosheets
with width of 10-15 nm and lengths of 200 nm were synthesized via a simple hydrothermal
23
method. The obtained nanosheets consisted of many nanometer-sized crystallites. The
nanosheets exhibit a strong blue emission and a weak red emission, while bulk Er2O3 has
almost no blue emission. [8] Lanthanide orthophosphate nanoparticles were synthesized via
sonochemical synthesis. The hexagonal LnPO4 (Ln= La, Ce, Pr, Nd, Sm, Eu, Gd) particles had a
nanorod-bundle morphology. They had a diameter of 100 nm and where about 500 nm long.
The tetragonal LnPO4 (Ln= Tb, Dy, Ho) particles had a sphere like morphology. The particles
were rather large. [9] Orthovanadate nanorods have also been reported. They were
synthesized via a hydrothermal route. The average diameters were 20 nm and lengths were
up to 100 nm. [10] Lanthanum sulfide nanoparticles were obtained via thermal
decomposition at lower temperature of a lanthanum complex (La(Et2S2CN)3·phen). The
diameters of the particles were between 10-30 nm. [11] LaF3:Ln3+ nanoparticles were
synthesized in methanol without using any ligands. The particles turned out to be highly
water-soluble. The diameter was about 12 nm. [12] Many other examples can be found in
literature.
To date, not many articles about lanthanide carbonate nanoparticles have been published.
The synthesis of Dy2(CO3)3 nanoparticles has been reported via sonochemical synthesis. The
nanoparticles were prepared by the reaction of Dy(OAc)3 with NaHCO3 in water and
irradiated with ultrasounds for 30 minutes. The Dy2(CO3)3 particles served as a precursor for
the synthesis of Dy2O3 nanoparticles. In the same article the authors also report the synthesis
of Dy(OH)3 nanotubes, but this synthesis was not based on Dy2(CO3)3 nanoparticles. After
washing and drying the Dy2(CO3)3 nanoparticles were calcinated in air at different
temperatures for 2 h. When the calcination temperatures were below 750 °C quasi-spherical
nanoparticles were obtained. From 800 °C the particles began to agglomerate. Following
decomposition pattern for the Dy2(CO3)3 nanoparticles was proposed:
Dy2(CO3)3·1,7 H2O Dy2(CO3)3
Dy2O2CO3
Dy2O3
24
XRD analysis confirmed that Dy2(CO3)3 had been synthesized. After calcinating the Dy2(CO3)3
samples at 500 °C two crystalline phases formed: dysprosium oxide and dysprosium oxide
carbonate. The samples calcinated at 650 °C formed pure Dy2O3 with cubic bixbyite phase,
also known as the C-rare-earth sesquioxide structure. TEM-images of Dy2(CO3)3 and Dy2O3 are
given in Figure 1. The Dy2O3 nanoparticles are spherical and their size varies between 15-20
nm. Photoluminescence spectra of the Dy2O3 nanoparticles were taken. There were two
emission peaks. One at about 17540 cm-1 (yellow emission) corresponding to an electron
transition of 4F9/2→6H13/2 and another at about 20700 cm-1 (blue emission) resulting of an
electron transition of 4F9/2→6H15/2. [13]
Europium doped gadolinium carbonate particles were synthesized using urea in a flask
reaction at 85 °C. The particles were spherical and monodisperse until reaction times of 240
minutes. The average diameter changed depending of the reaction time from 164 nm for 120
minutes to 240 nm for 240 minutes. At longer times platelet-shaped particles began to form
and eventually the spherical particles disappeared. At a reaction time of 420 minutes only
Figure 1: TEM images of (a) Dy2(CO3)3 (b) Dy2O3 [13]
Figure 2: TEM image of Gd(CO3)3:Eu at different reaction times (t6=120 min, t10=180 min, t12=240 min, t13=270 min, t14=300 min, t16=420 min) and a TEM image and the electronic diffraction pattern of a t6-annealed sample [14]
25
platelet-like particles existed. Figure 2 (t6-t16) shows TEM images of the particles at different
reaction times. The platelet-shaped particles appeared to be crystalline Gd(CO3)3·(2-3)H2O.
The substance was analyzed with WAXS (wide angle X-ray scattering), TGA (thermo
gravimetric analysis), FTIR (Fourier transform infrared spectroscopy) and PL
(photoluminescence). At a reaction time of 120 minutes amorphous Gd2(OH)(CO3)2 was
formed while at reaction times between 120 minutes and 420 minutes mixtures of
amorphous and crystalline particles were obtained. In the samples containing amorphous
phases the emission lines of Eu3+ were broad in comparison with the crystalline sample. The
amorphous sample (reaction time 120 minutes) was annealed at 850 °C for 4 h. Spherical,
uniform, non-agglomerated and crystalline Gd2O3 nanoparticles were obtained. The size is
about 10-50 nm as can be seen from the TEM shown in Figure 2 (t6-annealed). The Eu3+
emission spectrum has well defined lines as expected for a crystalline powder. [14]
La2(CO3)3 nanowires have been synthesized using a reversed micelles system consisting of
Triton X-100/cyclohexane/water. Triton X-100 is a nonionic surfactant. Using XRD and SAED
patterns the nanostructures proved to be of the orthorhombic type. However the diffraction
peaks were broad. This could be due to the fact that the nanowires were made up of some
disordered small-size nanocrystals near the axis with some ordered large ones around the
surface. Some reaction parameters were investigated. La2(CO3)3 nanowires could be obtained
at pH 2-5. When the pH exceeded 7 no nanowires were obtained. Also morphological
changes of the products due to the aging time and the influence of the aging temperature
were investigated. With an increase in aging time the length of the nanowires increased, this
can be seen in Figure 3. All nanowires in Figure 3 were prepared at aging temperature of 303
Figure 3: TEM image of the La2(CO3)3 nanowires at different aging times (a) 6h (b) 3h (c) 48h; aging temperature 303 K [15]
26
K. In Figure 4 the aging temperatures were held at 293 K and 313 K. When the aging
temperature was lower than 303 K nanobelts or flakelike nanowire bundles were formed.
When the aging temperature was increased the nanostructures became shorter and the
diameter became larger. [15]
La2(CO3)3 nanoparticles were also obtained via a sonochemical method. Different irradiation
times were used, but an irradiation time of 30 min was found to give best results. These
La2(CO3)3 nanoparticles were used to synthesize La(OH)3 nanoparticles and La2O3
nanoparticles. To prepare the La(OH)3 nanoparticles a water-based solution of La2(CO3)3
particles and N2H4 was hydrothermally treated for 24 h at 110 °C. To obtain La2O3
nanoparticles the La2(CO3)3 nanoparticles were calcinated at 600 °C for 2 h. The proposed
decomposition pattern was supported by a TGA analysis:
La2(CO3)3·1,7H2O La2(CO3)3
La2O2CO3
La2CO3
The XRD pattern showed that the La2(CO3)3 nanoparticles were of the orthorhombic type.
TEM images of the La2(CO3)3, La(OH)3 and La2O3 nanoparticles are given in Figure 5. The
La2(CO3)3 particles were spherical with sizes between 25 to 35 nm and showed a tendency to
agglomerate. The sizes of La(OH)3 particles were about 16-20 nm. The La2O3 particles were
30 nm in size with spherical shape. Further evidence for the composition of the particles was
provided by XPS (X-ray Photoelectron Spectroscopy), FTIR and EDS (Energy Dispersive
Spectrometry). The effect of the calcination temperature was investigated for the synthesis
of La2O3 particles. The results revealed that the mean particle size increased with increasing
temperature. Spherical nanoparticles were obtained when the calcination temperature was
Figure 4: TEM image of La2(CO3)3 nanostructures at aging temperature (a) 293 k (b) 313 K; reaction time 48h [15]
27
below 700 °C, but when the temperatures were higher the particles started to agglomerate.
[16]
2.2 Core/shell nanoparticles
Core/shell nanoparticles are gaining a lot of attention. These nanostructures consist of a core
and a shell made of two different materials. They usually have dimensions in the range of 20-
200 nm and the core/shell structure improves their properties. Choosing an appropriate
ligand can prevent agglomeration of the particles and thus improve monodispersity as well as
thermal or chemical stability and solubility. The shell can make the particles less cytotoxic
and can make it possible to conjugate other (bio)molecules to the particles. Also oxidation of
the core material can be prevented due to the shell. There are several possibilities in
choosing a core/shell structure. The core or the shell or both can be made of inorganic
materials. One can use metals, semiconductors or lanthanides. A widely used core/shell
nanostructure is a gold core with a silica shell. These core/shell nanoparticles find
applications in optical sensing. The optical properties of these gold nanoparticles can be
changed by changing the thickness of the silica shell. The silica shell also ensures that the
particles are biocompatible. Another well-known example is quantum dots (QD). These
contain semi-conducting materials and are usually an alloy of group 3 and group 5 metals or
group 2 and group 6 metals. CdSe/CdS, CdSe/ZnS, ZnSe/ZnS, CdTe/CdS core/shell
nanoparticles can be used for bio-imaging. The emission range of the particles is determined
by the shell thickness. Examples of lanthanide particles include YF3/silica or TiO2:Eu
nanoparticles. Aside from using inorganic materials also organic materials or even polymers
can be used. The organic material can form either the core or the shell of the particle. [17]
Figure 5: TEM image of (a) La2(CO3)3 (b) La(OH)3 (c) La2O3 [16]
28
Usually an inorganic core with an organic ligand is chosen. Often, for Ln3+ based core/shell
nanoparticles negatively charged ligands are used. Assuming that the overall charge of the
nanoparticles is equal to zero, there must be a larger excess then 1:3 of the Ln3+-ion relative
to fluoride in the case of synthesizing LnF3 nanoparticles. [18] At present the bonding
between the inorganic core and the organic shell is not fully understood. More research is
still needed, but core/shell nanoparticles like this are interesting. One can dope lanthanide
ions into the inorganic part of the particles (the core). Thanks to this the Ln3+ ions are
protected from the (organic) environment which reduces quenching. To enhance
dispersibility an organic shell is used. Depending on the chosen ligand the particles will be
dispersible in organic solvents or in water. One can also use the shell to facilitate
biofunctionalization. The luminescence properties of the lanthanide ions in nanoparticles are
very similar to those of bulk materials. [4, 19] The most used ligands for preparing Ln3+-doped
nanoparticles dispersible in organic media are oleic acid [20-24] and ammonium di-(n)-
octadecylditiophophate. [4, 25-27] Oleic acid stabilized nanoparticles can be made water
soluble by oxidizing the oleic acid and so generating free carboxylic acid groups at the
surface. [23] Ligand-exchange can also be used to convert hydrophobic core/shell
nanoparticles into hydrophilic ones. [24, 28, 29] There are also examples of other ligands
used in the synthesis of core/shell nanoparticles dispersible in organic solvents. [30, 31]
Although particles coated with such ligands are very interesting, water-based systems have
several advantages to organic solvent-based systems. A water-based system could be
considered as a ‘green chemistry’ alternative for producing nanoparticles. One does not need
to work with a toxic organic solvent and usually the synthesis is quite simple, safe and does
not require special atmospheric conditions. Further there will be a larger potential for large-
scale production. [32] Probably the most used ligand for water soluble nanoparticles is
citrate. [3, 22, 32-37] In addition to the use of organic ligands, there are also examples where
polymers are used as coating material. Used hydrophilic polymers include PVP
(polyvinylpyrrolidone), PAA (polyacrylic acid), PEG (polyethylene glycol) and PEI
(polyethylenimine). [38-42] In many cases it has been reported that the used ligand also
influences the morphology and size. In general the particles are smaller and more uniform
29
then the ones synthesized in absence of an organic ligand. [20, 32-34, 43-47] Lanthanide
fluoride materials as core within core/shell nanoparticles are popular because these
materials have a low phonon energy (low vibrational energy). This is caused by the high
ionicity of the Ln-F bond and as a consequence quenching of the luminescent Ln3+-ions is
minimal. [45] Van Veggel et al. has done a lot of work in the area of water soluble core/shell
lanthanide nanoparticles. The synthesized inorganic core, which is mostly LaF3, is doped with
luminescence Ln3+ ions. Different ligands are used for the organic shell. Citrate is most
commonly used [3, 22, 35, 36], but other ligands for example 2-aminoethyl phosphate (AEP)
are also used. [35, 36, 48] The synthesis of silica-coated LaF3:Ln3+ nanoparticles starting from
LaF3:Ln3+ citrate stabilized nanoparticles was demonstrated. Bioconjugation to avidin (a
biotin-binding protein) was possible. [49] In that same year bioconjugation to avidin was
demonstrated starting from AEP-stabilized nanoparticles. [50] LaF3 as core material was also
chosen by other groups for synthesizing water-soluble core/shell nanoparticles. Different
ligands were used. [45, 51, 52] There are also reports of the use of biomolecules like D-
glucose or chitosan using a LaF3 core. [53, 54] Other fluoride based materials as core like
GdF3 [35, 36], YF3, [40] EuF3, [33] NaYF4 [38, 39, 41] and LnF3, [34] were also reported. Besides
fluoride materials other inorganic cores such as YPO4, [32] YVO4 [37, 42, 55] and LnVO4 [43]
were used with a variety of ligands.
Yb3+–Er3+ co-doped LaF3 nanocrystals coated with glucose were synthesized in a flask reaction
at 60 °C for about 5 days in water as solvent. However, after about 90 minutes, dissolvable
Yb3+-Er3+ co-doped LaF3 particles were obtained in a clear solution. TEM images of the
hexagonal nano-crystals are shown in Figure 6. The particles adopt more or less rectangular
shapes. Their average size is about 15–20 nm and the surfaces of the particles are relatively
smooth. The influence of the pH was investigated. If the pH was higher than 10, the particles
could be completely precipitated. This was used to separate the particles. However if the pH
was lower than 7 the particles were dispersible. According to the authors a possible
explanation is the equilibrium between the two structural forms of glucose (cyclic and
acyclic). The cyclic form is predominant when the pH value is more than 7. Upconversion
fluorescent spectra of the nanoparticles were measured and the particles excited at 980 nm
30
showed red and green luminescence. Coating of the particles with silica was possible without
altering the shape. These particles were found to have potential as up-conversion fluorescent
labeling materials. [53]
Lanthanide orthovanadates (LnVO4, Ln=Y, Dy, Er, Ce, Gd) were synthesized using sodium
citrate (Na3cit), sodium tartrate (Na2tar) and sodium malate (Na2mal) as ligands. The
synthesis was a hydrothermal process at 140 °C mostly carried out for 24 h with varying
amounts of the complexing agent. Depending of the synthesis conditions different
morphologies were obtained. For example YVO4 nanopersimmons were obtained with 2:1
molar ratio of cit3-/Y3+ at 140 °C for 24 h. A SEM image is shown in Figure 7 a. The particles
are uniform and have a concave dip in their center. The individual YVO4 architectures are
composed of many smaller nanoplates (Figure 7 b and Figure 7 c). The influence of the
reaction time, the amount of ligand and different complexing agents were investigated. It
was found that nanocubes instead of nanopersimmons were obtained when Na2tar was used
as a ligand under similar reaction conditions. This can be seen in Figure 7 d. The obtained
products also have a uniform morphology and are composed of numerous nanoplates. There
is a shallow concave dip in the each face of the nanocubes (Figure 7 f). Using Na2mal as the
complexing agent, under similar reaction conditions, yielded irregular nanoparticles (Figure
8). Therefore it has been found that the complexing agent has great effect on the
morphology of the product. The optical properties of YVO4 nanopersimmons of various sizes
were studied. [43]
Figure 6: TEM images of the LaF3/glucose nanoparticles [53]
31
Coating nanoparticles with AEP gives them a positively charged surface at physiological pH.
Highly water-soluble GdF3 or GdF3/LaF3 nanoparticles stabilized with AEP were synthesized in
a flask reaction at 75 °C for 3-4 h. AFM measurements show that the particles had a broad
size distribution (shown in Figure 9). The typical cross-sectional diameter was 51,5 nm as
determined by DLS. The particles are promising as relaxation agents in NMR studies. [35]
Undoped and La3+-doped LnF3 nanoparticles stabilized with AEP were prepared using a
similar method as described above. The sizes varied between 3-10 nm. [36] Using AEP as a
ligand, biotin moieties could be attached on the surface of Ln3+-doped LaF3 nanoparticles.
Due to this binding to avidin was made possible. Avidin is a biotin-binding protein that can be
found in the egg white of birds, reptiles and amphibians. The interaction of biotin and avidin
is the strongest known non-covalent interaction between a protein and ligand. In this case it
Figure 8: TEM image of YVO4 nanoparticles obtained when
using Na2mal as capping ligand [43]
Figure 7 a) Low-magnification SEM image of monodisperse YVO4 nanopersimmons obtained with Na3cit; b) enlarged SEM image of YVO4 nanopersimmons; c) SEM image of an individual YVO4
nanopersimmon; d) Low-magnification SEM images of monodisperse YVO4 nanocubes obtained with Na2tar; e) enlarged SEM image of YVO4 nanocubes; f) SEM image of an individual YVO4 nanocube [43]
32
is used to test the ability of the biotinylated particles to be bound to a biological system. [50]
Water-soluble LaF3:Eu/AEP nanoparticles were synthesized in a low temperature flask
reaction. The reaction was performed at 37 °C for 72 h. The XRD pattern showed broad peaks
which indicate a low crystalline sample. DLS revealed an average radius of 232 nm, but a
large polydispersity. These nanoparticles were shown to react with 6-carboxy-5’-methyl-2,2’-
bipyridine (bipyCOO-) in water. Analysis pointed to a partial displacement of AEP molecules
at the surface, but the overall morphology of the nanoparticles was maintained. TEM images
of the AEP-stabilized and of the 6-carboxy-5’-methyl-2,2’-bipyridine stabilized nanoparticles
are shown in Figure 10. The Eu3+ luminescence was improved up to two orders of magnitude
due to the very efficient light harvesting of the surface-bonded 6-carboxy-5’-methyl-2,2’-
bipyridine. [51]
2.3 Possible application of water soluble core/shell nanoparticles
Luminescence labeling of biomolecules has been recognized as a valuable tool in biological
studies. The more commonly used types of fluorescent labels are being replaced by newer
types like inorganic nanoparticles or fluorescent latex/silica nanobeads. Conventional
Figure 10: TEM image of LaF3:Eu stabilized with AEP (left) and LaF3:Eu stabilized with bipyCOO- (right) [51]
Figure 9: AFM image consisting of nanoparticles of an 80/20 mixture of
GdF3 and LaF3 stabilized with AEP [35]
33
fluorescent labels like organic dyes, fluorescent proteins and lanthanide chelates have their
advantages like small sizes, high water solubility, easy usage and existing standard protocols
for their bioconjugation. However they have several limitations. Usually they have a broad
spectrum; they are sensitive to photobleaching and have a low photochemical stability.
Organic fluorophore-tagged fluorescent latex nanobeads can solve these problems. A
nanobead consists of a polymer shell which encapsulates thousands of fluorophores. Thanks
to this the fluorophores are protected from the environment and more stable against
photobleaching. Also more light is emitted due to the large number of fluorophores.
Unfortunately polymer coated nanoparticles also face some problems such as larger particle
size, swelling, agglomeration and leaking of the fluorophore through surface defects. A
newer and more popular encapsulating material is silica. It can encapsulate organic and
inorganic dyes as well as lanthanide chelates. Silica enhances water solubility, improves
stability and protects from photobleaching. Silanol groups on the surface of the nanobeads
allow conjugation of biomolecules. [19]
In the class of inorganic nanoparticles semiconductor quantum dots and lanthanide doped
compounds have received most attention. Quantum dots (QD) as mentioned previously are
generally composed of group 3 and group 5 metals or of group 2 and group 6 metals. Usually
they have dimensions between 1 and 5 nm. This size is in the same order of magnitude as the
De Broglie wavelength of electrons and holes at room temperature. Due to this fact the
states of the free charge carriers in quantum dots are quantized and their movement is
determined by quantum mechanics. This leads to unique optical and electronic properties
that are dependent on the particle size. Because uncapped quantum dots were unstable and
their emission was rather weak research shifted to core/shell quantum dots with a higher
quantum yield and a better stability. The University of Ghent has some expertise in core/shell
quantum dots dispersible in organic media provided by Prof. Dr. Zeger Hens. [56-59] The
insolubility of quantum dots in aqueous media limits their potential applications in biological
systems. If possible, ligand exchange could be an outcome. Alivisatos and Nie demonstrated
that quantum dots could be made water soluble and bioconjugated. [60, 61] Thus,
applications were extended to the biological field. Using quantum dots in biological fields
34
have some advantages. They have a greater sensitivity and stability then conventional
organic fluorophores. The wavelength of emission can be tuned varying size and composition
of the quantum dots. Their excitation is quite easy and their emission of light is slow enough
to eliminate most autofluorescence in the background. However, they do have some
limitations. They exhibit optical blinking which makes application in quantitative assays
difficult. The quantum dots themselves are not biocompatible and they have to be surface
modified. [19] Lanthanide doped compounds are another promising class of luminescent
nanoparticles for biological applications. Water soluble lanthanide nanoparticles can be
obtained by directly synthesizing core/shell particles or by modifying the surface of already
synthesized nanoparticles. They usually have a quite good quantum yield. Using the right
organic ligand facilitates bioconjugation. The luminescence of such particles is characterized
by narrow emission bandwidths. The emission bands are determined by the lanthanide ions
used. The emission and absorption lines from each lanthanide ion in the nanoparticles do not
overlap, neither are they influenced by the particle size. This offers multiplexing capabilities.
Optical properties can be tuned depending on the doped ions. These particles possess a high
photochemical stability, they are strongly fluorescent and have long fluorescence lifetimes.
Further, low toxicity, large effective Stokes shifts and sharp emission band widths (10-20 nm)
are advantageous. [19, 50] There are several examples of bioconjugation or biological
applications of lanthanide doped nanoparticles, however more research is needed. [19, 50,
54, 62, 63]
35
3 Equipment and used chemicals
The chemicals used were lanthanum nitrate (La(NO3)3·6 H2O) 99,99% purchased from Roth,
urea (CH4N2O) pro analysis, hydrochloric acid fuming 37% for analysis (HCl) purchased at
Merck, anhydrous α-D-glucose (Gluc, C6H12O6), malic acid (MA, C4H6O5) 99%, 2-aminoethyl
phosphate (AEP, C2H8NO3P), sodium fluoride (NaF) 99%, lanthanum acetate (La(OAc)3·1,5
H2O) 99,99%, gadolinium nitrate (Gd(NO3)3·6 H2O) 99,99%, yttrium nitrate (Y(NO3)3·6 H2O)
99,99% and aqueous ammonia solution (NH3(aq)) 30% purchased via Sigma Aldrich.
Anhydrous sodium carbonate (Na2CO3) was acquired via UCB. Methanol (MeOH) and ethanol
(EtOH) AnalaR NORMAPUR were purchased from VWR. Sodium hydroxide 98% (NaOH) was
obtained via Chemlab. All chemicals were used without further purification.
3.1 Diffuse Reflectance infrared Fourier transform spectroscopy
(DRIFTS)
Fourier transform spectroscopy (FTIR) is a well-known technique. Atoms in molecules and
solids vibrate. This vibrational motion is quantized and at room temperature most of the
molecules are in their lowest vibrational state. The absorption of infrared light can excite
these molecules to a higher vibrational level. This absorption of infrared light in function of
wavelength gives rise to an infrared spectrum. The vibrations can be divided according to the
type of movement of the atoms in a molecule. Stretching vibrations (bond
lengthening/shortening) and bending vibrations (change in bond angle) are known.
Directing infrared radiation onto the surface of a solid sample gives rise to two types of
reflected energy. Specular reflectance is the radiation which reflects directly off the sample
surface. Diffuse reflectance is the radiation which penetrates into the sample and then
emerges. A diffuse reflectance accessory is designed so the diffuse reflected energy is
optimized. KBr acts as a non-absorbing matrix.
DRIFTS spectra were recorded with a Thermo Scientific FT-IR spectrometer (type Nicolet
6700) equipped with a DRIFTS-cell. Prior to the measurements a background measurement
using KBr is performed. KBr is further used as background by mixing it with the sample. The
36
sample is ground to reduce the particle size to less than 5 mm in diameter, otherwise, large
particles scatter the infrared beam. The Kubelka-Munk theory is used and for each sample a
spectrum from 700 cm-1 to 4000 cm-1 with a resolution from 4 cm-1 is recorded.
3.2 Transmission electron microscopy (TEM)
A beam of accelerated electrons is directed at a very thin sample and the transmitted
electrons are detected. Two modes can be used: the image mode and the diffraction mode.
In the case of the image mode an image of the material is formed. The formation of the
image is based on the same principle as an optical microscope, but this technique provides a
higher resolution. In the diffraction mode the diffraction pattern is visualized. Also chemical
analysis can be performed using TEM. Characteristic X-rays are formed due to the interaction
between the electrons and the sample which can be detected. Electron energy loss
spectroscopy (EELS) can be performed. Usually TEM is used for imaging purposes.
The TEM used was a JOEL JEM2200FS transmission electron microscope with an accelerating
voltage of 200 kV. Images were obtained digitally on a Gatan CCD camera. The samples for
TEM were prepared on copper grids (size 200 mesh) coated with a carbon support film. The
samples were prepared by placing a drop of aqueous solution of the product on a grid and
allowing the solvent to evaporate.
3.3 Scanning electron microscopy (SEM)
A beam of accelerated electrons is scanned across the sample. In SEM measurements the
energy of the electrons is in typically lower than in the case of TEM measurements. The
sample is also thicker. Different signals can be detected: secondary electrons, backscattered
electrons and X-rays. Detecting secondary electrons results in an image with a large depth of
field. The image seems to be in 3D. Topographic images are obtained. Using backscattered
electrons inhomogeneities can be detected since the yield of the backscattered electrons is
dependent of the atomic number. Due to the interactions of the sample with the electrons X-
rays can be produced, which can be used for chemical analysis.
37
SEM measurements were performed with a FEI Quanta 200 F SEM and a FEI Nova 600
Nanolab Dual-Beam focused ion beam in secondary electron mode.
3.4 X-ray diffraction (XRD)
XRD is a non-destructive technique that reveals information about the chemical composition
and crystallographic structure of materials. It is based on the constructive interference of
monochromatic X-rays and a crystalline sample. When a monochromatic X-ray beam with a
certain wavelength is projected onto a crystalline material at an angle theta, diffraction at
the lattice of the crystal occurs. Constructive interference of these diffracted X-rays occurs
only when the conditions satisfy Bragg's Law (nλ=2d sin θ). These diffracted X-rays are then
detected, processed and counted. By scanning the sample through a range of 2θ angles, all
possible diffraction directions of the lattice should be achieved due to the random
orientation of the powdered material. By plotting the angular positions and intensities of the
resultant diffracted peaks a pattern is produced. This pattern is characteristic for the sample.
Analysis of the diffraction pattern can allow the identification of phases within a given
sample.
In this thesis only powder XRD is performed. Sample preparation is limited. The powder is
ground and placed into a sample holder. Care must be taken to create a flat upper surface.
XRD patterns were recorded by a Thermo Scientific ARL X’TRA diffractometer equipped with
a Cu Kα (λ = 1.5405 Å) source, a goniometer and a Peltier cooled Si(Li) solid state detector.
3.5 Elemental analysis (EA)
Elemental analysis is a process where a sample is analyzed for its elemental composition. A
very familiar technique is CHN analysis, which is a combustion analysis. The amount of
carbon, hydrogen and nitrogen in the sample is determined. The sample is first fully
combusted in an oxygen rich environment. The carbon, hydrogen and nitrogen present
oxidize and form CO2, H2O, N2 and NOx. All nitrogen containing products are finally reduced
to N2. These combustion products are analyzed.
38
For the analysis a Thermo Scientific* FLASH 2000 Series CHNS/O Analyzer is used. The
combustion reactor reaches 1800°C and a thermal conductivity detector is used.
3.6 Advanced luminescence set-up
Lanthanides are most known for their luminescence properties. The energy levels of the
lanthanides correspond closely to the free-ion levels. As a consequence the luminescence
spectra are characterized by sharp transitions. Energy levels of the lanthanide ions are
known. Using the luminescent set-up one can record emission spectra and excitation spectra.
Lifetimes can be determined.
For recording an emission spectrum one excites the product at the wavelength of maximum
absorption and one measures the luminescence. For lanthanides this is mostly in the visible
range or in the near-infrared. For life time measurements one measures how long the excited
states lives, so how long the ion is luminescent. This is highly dependent on the environment.
For the measurements a Double Edinburgh Instruments FLSP920 / FSP920 spectrometer
setup is used. It contains two systems. System 1 is a UV-VIS-NIR spectrometer. The system is
capable of measuring steady state and time-resolved emission in the wavelength range 200-
1700 nm (80 ps – several seconds), containing a Hamamatsu R928P PMT for the 200-900 nm
range and a Hamamatsu R5509-72 NIR PMT for the 300-1700 nm range. System 2 is a NIR-
MIR spectrometer, but this will not be used.
A 450W xenon lamp as the steady state excitation source is used. Emission and Lifetime
measurements were performed both in suspension and in powder. For preparing the
suspension 0,01 g of the product was dissolved in 2 ml water.
The Tb3+ emission spectra were recorded at an excitation wavelength of 351 nm from 450 nm
to 650 nm. The step size was 0,5 nm, the dwell time 0,5 s. For the suspensions the scan slit
was set to 0,5 nm and the fixed slit was set to 5 nm. For the solid samples the scan slit was
0,5 nm and the fixed slit 0,2 nm.
39
The Eu3+ emission spectra were recorded at an excitation wavelength of 395 nm from 550 nm
to 750 nm. The step size was 0,5 nm, the dwell time 0,5 s. For the suspensions the scan slit
was set to 0,3 nm and the fixed slit was set to 5 nm. For the solid samples the scan slit was
0,3 nm and the fixed slit 0,7 nm.
40
4 Uncoated lanthanum carbonate particles
All lanthanum carbonate nanoparticles were synthesized hydrothermally. Different reaction
times, reaction temperatures and different dilutions were employed. As carbonate source
urea and Na2CO3 were used. La(NO3)3 and La(OAc)3 were used as lanthanum source. The
reaction conditions of ZL 18 and ZL 28 were chosen to synthesize lanthanum carbonate
nanoparticles doped with Eu3+ and Tb3+.
After drying, white powders were obtained which were tested for their solubility in water. All
powders gave poorly stable white suspensions. The differences in stability were negligible.
XRD was used to determine the phase. After comparison with literature all hydrothermal
particles seemed to be LaCO3OH, which has two polymorphs. The first possible polymorph is
the hexagonal phase. The second polymorph is the orthorhombic phase. [64-67] The XRD’s
shown in Figure 11 match hexagonal LaCO3OH, no impurities could be detected. In the case
of the particles in Figure 12 it is possible that a mixture of the hexagonal phase and the
orthorombic phase has formed. In all cases we can see an additional peak at 20 degrees,
which is typical for LaCO3OH in the ortorhombic phase. In the case of ZL 24 and ZL 33 we can
notice an additional peak a little over 15 degrees. There are also some additional peaks
between 30 and 40 degrees which can be assigned to the ortorhombic phase. Several peaks
characteristic for the ortohombic phase overlap with the characteristic peaks for the
hexagonal phase.
41
Figure 11: XRD spectra of the uncoated particles, hexagonal phase
Figure 12: XRD spectra of the uncoated particles, mixed phases
There seems to be no clear pattern or explanation as for which polymorph forms. Neither the
lanthanum source nor the carbonate source seems to promote the formation of the
42
hexagonal or orthorhombic phase. Elemental analysis (Table 1) shows that only negligible
amounts of nitrogen are still present in the particles, so no nitrogen from urea or nitrates
builds in. The percentage of carbon and hydrogen in LaCO3OH is calculated. Values of 5,56 %
for carbon and 0,47 % for hydrogen are predicted. These results are in close agreement with
the results of the elemental analysis.
Table 1: elemental analysis of the uncoated lanthanum carbonate particles
DRIFTS spectra of different samples were taken. The samples were carefully chosen in order
to have every combination of lanthanum and carbonate source. The spectra are shown in
Figure 13
Figure 13:DRIFTS spectra of the selected LaCO3OH samples
As expected all the spectra were very similar. The peaks were assigned based on literature.
[16, 65, 67]. Absorption between 3400 and 3700 cm-1 is due to water or other OH-groups.
ZL 18 ZL 19 Predicted values
Nitrogen (%) 0,03 0,06 0
Carbon (%) 5,74 5,84 5,56
Hydrogen (%) 0,50 0,54 0,47
43
The peak around 3400 cm-1 is the result of adsorbed water (stretching vibration), the peak
around 3600 cm-1 is assigned to the OH-group of LaCO3OH. The peak at 2500 cm-1 is most
likely due to gaseous CO2. In the region around 1430–1500 cm-1 one should be able to
distinguish the ν3 mode of the carbonate. The second peak seen at 1500 cm-1 is assigned to
the same mode. Around 1080 cm-1, 840 cm-1 and 750 cm-1 the peaks of the ν1, ν2 and ν4
modes of the carbonate ion appear. Important in the infrared spectrum is the peak at 3600
cm-1 which confirms the formation of LaCO3OH instead of La2(CO3)3 particles.
The size and morphology of the particles were determined using TEM. When using La(NO3)3
as lanthanum source and Na2CO3 as carbonate source no good results were obtained. The
particles were very big and aggregated. Because they were so aggregated it was difficult to
determine their individual size, but one can no longer speak of nanoparticles with sizes
varying between 400-1000 nm.
Using urea as carbonate source improves the results. The reaction conditions are
summarized in Table 2. By comparing ZL 18 with ZL 21 and ZL 26 with ZL 28 the influence of
the amount of used solvent can be estimated. In each case the particles are agglomerated. In
the case of ZL 26 and ZL 28 the particles are so agglomerated that it is impossible to
determine their individual sizes. It is a mixture of big aggregated particles and smaller
particles. In the case of ZL 18 and ZL 21 the particles are also very big (at least 100 nm), but
less agglomerated. Dilution seems to have little influence. The influence of time on the
particles shape and size can be investigated comparing ZL 28 and ZL 31. The particles
obtained from synthesis ZL 31 are also aggregated. Again the particles are too agglomerated
to determine their individual sizes. The smaller particles which were present in sample ZL 28
have disappeared. This can be due to Ostwald ripening since longer synthesis times are
Figure 14: TEM image of ZL 18 (left) and ZL 21 (right)
44
applied in ZL 31. By comparing ZL 21 and ZL 31 one can see the influence of temperature. It
seems that lower temperatures improve the uniformity and agglomeration of the particles.
Overall there is little difference between the particles synthesized with urea and La(NO3)3.
One cannot pinpoint the influence of different reaction variables. The particles synthesized
using a water/ethanol mixture (ZL 24) were also very aggregated and big. Their individual
sizes could not be determined. Selected TEM pictures of the discussed particles are shown in
Figure 14.
The difference is striking when we replace La(NO3)3 with La(OAc)3. When using urea as
carbonate source good results were obtained. The particles from reaction ZL 19 (using urea
as a carbonate source) were a bit aggregated, but quite small. They had a rather broad size
distribution ranging from 20-60 nm. Repeating the same reaction for a shorter time (12 h
instead of 24 h) seemed to yield a little more aggregated, but still small particles (ZL 47).
Table 2: summarized reaction conditions of the selected samples
sample Amount of water (ml) Time (h) Reaction temperature (°C)
ZL 18 20 24 120
ZL 26 20 12 140
ZL 29 20 24 140
ZL 20 30 24 120
ZL 27 30 12 140
ZL 30 30 24 140
ZL 21 50 24 120
ZL 28 50 12 140
ZL31 50 24 140
45
Using Na2CO3 as carbonate source gave small, but very aggregated particles. TEM pictures of
ZL 19 and ZL 47 are shown in Figure 15.
In general it can be said that the worst results were obtained when Na2CO3 was used as
carbonate source. The biggest difference was seen when the lanthanum source was changed.
Other parameters seemed to have little influence for our purpose.
By adopting the synthesis condition of ZL 28 doped particles were synthesized. XRD spectra
showed that in each case the same product was formed (Figure 16). Luminescence
measurements were performed on suspensions and solid samples. The suspensions were
prepared by dissolving 0,01 g of the powder in 2 ml of water. The emission spectrum of the
suspension with doping percentage 10 % (ZL 42) is shown in Figure 17. The main emitting
level of Tb3+ is 5D4. Four transitions can clearly be distinguished. At 490 nm the 5D4→7F6
transition is observed, followed by the 5D4→7F5, 5D4→
7F4 and 5D4→7F3 transition at 540 nm,
580 nm and 620 nm respectively. The remaining emission spectra can be found in the
appendix. In general one can state that with increasing doping percentage an increasing
intensity in the emission spectra is observed. ZL 40 only has a distinct peak at 540 nm. This
can be assigned to the 5D4→7F5 transition which is normally the most intense. Most likely this
unclear emission spectrum is the consequence of the low Tb3+ concentration. The fact that
the intensity keeps increasing suggests that even at doping percentages of 10 % no self-
quenching effects occur.
Figure 15: TEM image of ZL 19 (left) and ZL 47 (right)
46
Figure 16: XRD spectra of the Tb3+-doped samples using the synthesis conditions of ZL 28
Figure 17: emission spectrum of ZL 42 (10% Tb3+) in suspension
47
Lifetime measurements were performed (Table 3). ZL 40 clearly has a lower lifetime then the
other samples. Considering the low intensity and low lifetime 0,1 % is not an ideal doping
concentration. For other doping percentages a lifetime of 1,5 ms is obtained.
Table 3: measured lifetimes of the Tb3+ particles in suspension synthesized accoriding to ZL 28
Sample Lifetime
(ms)
ZL 40 / 0,1 % Tb3+ 1,3
ZL 41 / 1 % Tb3+ 1,5
ZL 36 / 2 % Tb3+ 1,5
ZL 35 / 5 % Tb3+ 1,5
ZL 42 / 10 % Tb3+ 1,5
The emission spectrum of sample ZL 42 in the solid phase is shown in Figure 18. The
remaining spectra can be found in the appendix. Also in this case the intensity increases with
an increasing doping percentage. Lifetime measurements (Table 4) were performed and on
average a lifetime of 1,6 ms was obtained. In general the solid samples show a bit higher
lifetimes, but the difference is very small as expected. The goal was to embed the lanthanide
ions in an inorganic matrix to reduce quenching effects. In suspension the Tb3+-ions at the
surface will be subjected to quenching from the surrounding water, but this effect disappears
in the solid phase which explains a slightly higher lifetime.
Table 4: measured lifetimes of the Tb3+ particles in the solid phase synthesized accoriding to ZL 28
Sample Lifetime
(ms)
ZL 40 / 0,1 % Tb3+ 1,4
ZL 41 / 1 % Tb3+ 1,6
ZL 36 / 2 % Tb3+ 1,6
ZL 35 / 5 % Tb3+ 1,6
ZL 42 / 10 % Tb3+ 1,6
48
Doped nanoparticles were also synthesized using the synthesis conditions of ZL 18. The
nanoparticles were doped with Tb3+ and Eu3+. XRD spectra of the Tb3+-doped particles show
that the formed phase alters in this case (Figure 19). A peak at 20 degrees can be
distinguished as well as some additional peaks between 30 and 40 degrees. The XRD
spectrum now matches the XRD spectrum of ZL 28 more closely. Reaction ZL 18 was
repeated, but the XRD did not show the additional peaks. There are two plausible
explanations: doping the particles influences the formed phase in some way or since the
intensity of the peak at 20 degrees shows strong variations in intensity (Figure 12) it could be
that the peak was lost in the noise previously.
Figure 18: emission spectrum of ZL 42 in the solid phase (10% Tb3+)
49
Figure 19: XRD spectra of the Tb3+-doped samples using the synthesis conditions of ZL 18
The recorded emission spectra are similar to the previous doped Tb3+ nanoparticles. The
emission spectra were recorded both in suspension (0,01 g in 2 ml) and solid phase. In the
case of the suspension the 5D4→7F6 transition occurs at 490 nm, the 5D4→
7F5, 5D4→7F4 and
5D4→7F3 transition are observed at 540 nm, 580 nm and 620 nm respectively. The intensities
increase until ZL 51 (10 % doping percentage) and after that they stagnate. The emission
spectrum of ZL 51 is shown in Figure 20. The remaining spectra can be found in the appendix.
50
Figure 20: emission spectrum of ZL 51 (10% Tb3+) in suspension
Lifetime measurements were conducted and are summarized in Table 5. Lifetimes increase
until a maximum value of 1,6 ms (ZL 50, ZL 51, ZL 52) after which they decrease until 1,4 ms.
Table 5: measured lifetimes of theTb3+ particles in suspension synthesized accoriding to ZL 18
Sample Lifetime (ms)
ZL 49 / 2 % Tb3+ 1,5
ZL 50 / 5 % Tb3+ 1,6
ZL 51 / 10 % Tb3+ 1,6
ZL 52/ 12 % Tb3+ 1,6
ZL 53 / 15 % Tb3+ 1,5
ZL 54 / 20 % Tb3+ 1,4
The spectrum of sample ZL 51 measured in the solid phase is shown in Figure 21. The
spectrum is comparable with the spectrum measured in suspension.
51
Figure 21: emission spectrum of ZL 51 in the solid phase (10% Tb3+)
Lifetime measurements were performed (Table 6). Again the lifetimes in the solid state are
somewhat higher than in suspension due to reduced quenching.
Table 6: measured lifetimes of the Tb3+ particles in the solid phase synthesized accoriding to ZL 18
Sample Lifetime
(ms)
ZL 49 / 2 % Tb3+ 1,5
ZL 50 / 5 % Tb3+ 1,6
ZL 51 / 10 % Tb3+ 1,7
ZL 52/ 12 % Tb3+ 1,7
ZL 53 / 15 % Tb3+ 1,7
ZL 54 / 20 % Tb3+ 1,6
From the results it can be concluded that doping percentages around 10% are preferable.
They provided good intensities and the longest lifetimes in this series.
On irradiation with UV-light green luminescence of the obtained powders and suspensions
could be visualized (Figure 22)
52
Figure 22: a suspension of ZL 51 (left) and the powder of ZL 51 (right) under UV-radiation
The Eu3+ doped nanoparticles were also measured in suspension (0,01 g in 2 ml of water) and
in solid phase. The XRD spectra of the formed products are shown in Figure 23. In contrary to
the Tb3+-doped samples these XRD spectra match the XRD spectrum of ZL 18 closely. In some
of the spectra there are some additional peaks between 30 and 40 degrees, but these are
quite small.
Figure 23: XRD spectra of the Eu3+-doped samples using the synthesis conditions of ZL 18
53
The emission spectrum of ZL 59 (15 % Eu3+) in suspension is shown in Figure 24. The
remaining spectra can be found in the appendix. 5D0 is the main emitting level of Eu3+. At 580
nm the 5D0→7F0 transition is observed, at 590 nm the 5D0→
7F1 transition is visible. 3 peaks
can be seen, the large splitting indicates low symmetry. Next at 617 nm the 5D0→7F2
transition is observed. The intensity of the peak is quite large which again is an indication of
low symmetry. The 5D0→7F3 and 5D0→
7F4 transitions can be seen at 652 nm and 690 nm
respectively.
Figure 24: emission spectrum of ZL 59 (15% Eu3+) in suspension
The obtained lifetimes are summarized in Table 7. On average a lifetime of about 600 μs is
obtained.
54
Table 7: measured lifetimes of the Eu 3+ particles in suspension synthesized accoriding to ZL 18
Sample Lifetime
(μs)
ZL 55 / 2 % Eu3+ 620
ZL 56 / 5 % Eu3+ 620
ZL 57 / 10 % Eu3+ 580
ZL 58/ 12 % Eu3+ 610
ZL 59 / 15 % Eu3+ 580
ZL 60 / 20 % Eu3+ 540
In Figure 25 the emission spectrum of ZL 59 in solid phase is shown. It is very similar to the
previous one. Again the large splitting of the peaks indicates low symmetry.
Figure 25: emission spectrum of ZL 59in the solid phase (15% Eu3+)
As expected the lifetimes measured in the solid phase (Table 8) are a bit higher.
55
Table 8: measured lifetimes of the Eu 3+ particles in the solid phase synthesized accoriding to ZL 18
sample Lifetime
(μs)
ZL 55 / 2 % Eu3+ 660
ZL 56 / 5 % Eu3+ 660
ZL 57 / 10 % Eu3+ 650
ZL 58/ 12 % Eu3+ 620
ZL 59 / 15 % Eu3+ 620
ZL 60 / 20 % Eu3+ 620
Also in this case luminescence of the obtained powders and suspensions could be visualized
under UV-radiation (Figure 26).
Figure 26: a suspension of ZL 59 (left) and the powder of ZL 59 (right) under UV-radiation
56
5 Synthesis of lanthanum carbonate particles in presence of 2-
aminoethyl phosphate (AEP)
During the synthesis La(NO3)3 was used as lanthanum source
and Na2CO3 (AEP 11 and AEP 17) or urea (AEP 19) were used
as carbonate source. The AEP (Figure 27) solution was first
neutralized and a flask reaction for 2 or 3 hours was
performed. In each case clear solutions were obtained. When
the synthesis was repeated without carbonate source (AEP
20), a white suspension was obtained. The products were precipitated and washed with
ethanol or methanol and collected by centrifugation.
After the products were collected and dried, they were resuspended. AEP 11, AEP 17 and AEP
19 yielded clear solutions after resuspending them in water, but the Tyndall effect could not
be observed. AEP 20 yielded a white, unstable suspension.
The XRD spectra (Figure 28) of the obtained products are all quite similar except the one of
AEP 20. The spectra show that the samples are not very crystalline. AEP 20 seems to be a
little more crystalline, but the spectrum contains a lot of noise. Neither characteristic peaks
of lanthanum carbonate nor lanthanum hydroxycarbonate could be distinguished in any of
the spectra. Probably a complex between AEP and lanthanum is formed instead of core/shell
nanoparticles. TEM measurements confirmed the absence of nanoparticles in the solutions.
Figure 27: 2-aminoethyl phosphate (AEP)
57
Figure 28: XRDs of AEP 11, AEP 17, AEP 19 and AEP 20
Elemental analysis was performed (Table 9) and from these results it can be concluded that
no additional carbon builds in when a carbonate source is used. This also suggest that no
carbonates were formed during the reaction of La(NO3)3 with Na2CO3/urea in the presence of
AEP. The nitrogen originates probably from the ligand, lanthanum source, urea or
ammonium (used to neutralize the AEP-solution). AEP 11 contains less nitrogen then AEP 19,
perhaps due to the difference in carbonate source. In the case of AEP 20 no carbonate source
is used, still this product contains a lot of nitrogen. This can be explained by the fact that
maybe more AEP-molecules can bind to the La-ion forming a complex (no carbonate ions are
present), but also NH3(aq) can play a significant role. It has been previously stated in literature
that NH4+ builds into the nanoparticles to provide charge balance. The nitrates from the
lanthanide source did not build in. [3]
58
Table 9: elemental analysis of the obtained products synthesized in the presence of AEP
AEP 11 AEP 19 AEP 20
Nitrogen 5,90 8,67 10,06
Carbon 9,64 10,24 9,87
Hydrogen 3,32 3,69 3,19
A DRIFTS spectrum of AEP is recorded (Figure 29) and the peaks are assigned with help of
literature. [68]
Figure 29: DRIFTS spectrum of AEP
H2AEP has a zwitterion character. Bands that can be assigned to NH3+ vibrations can be found
between 3000-2800 cm-1 (broad band), 2800-2000 cm-1 (combination bands and overtones)
and between 1600 and 1500 cm-1 (δas and δs). The bands between 900 and 1000 cm-1 are the
symmetric stretching modes of the PO3 group and the bands between 1000 and 1200 cm-1
are the asymmetric stretching modes of the PO3 group. In complexes these bands can appear
over a narrower range of frequencies. The P=O stretching frequency can be found between
1350 cm-1 and 1175 cm-1. The rather broad band around 3000 cm-1 can be assigned to water.
The DRIFTS spectra of AEP 11 and AEP 19 (Figure 30) closely resemble each other, which
indicates that the carbonate source has little influence. The peaks of AEP 11 are broader, but
this can be due to sample preparation. Water contributes at the broad band around 3500
59
cm-1. CO32- bands should be found between 1500-1410 cm-1 and between 1100-700 cm-1. In
this region a lot of peaks of AEP can be found, which makes it difficult to distinguish possible
carbonate peaks. Especially in the spectrum of AEP 19 characteristic AEP peaks are
recognized. The bands seem to appear in a narrower range, but this can be due to
complexation.
Figure 30: DRIFTS spectrum of AEP 11 and AEP 19
The DRIFTS spectrum of AEP 20 (Figure 31) does not differ a lot from AEP 19 and AEP 11. The
peaks of AEP are quite recognizable. The PO3 vibrations appear over a bit narrower range,
probably as the consequence of complexation. However based on elemental analysis it is not
possible to come up with any feasible formula of a La-AEP complex. The solubility of AEP 20
was tested in different solvents (water, ethanol, dichloromethane, chloroform and butanol),
but the product was not dissolvable in any of the tested solvents.
60
Figure 31: DRIFTS spectrum of AEP 20
The exact composition of the formed products could not be determined. Most likely no
(core/shell) particles were formed. Although there are indications that AEP 20 is different
from all the other products, it was not possible to pinpoint the exact difference. It can be
established that no uncoated carbonate nanoparticles were formed during the reaction
either. A reasonable explanation is that AEP is a very strong ligand, therefore the carbonate
ions can hardly compete with the ligand to from a bond with the lanthanum ions. The
presence of the carbonate ions does influence the reaction as can be determined from the
results, but the precise influence could not be elucidated. It could be that in the case of AEP
20 only a more crystalline complex is formed.
61
6 Synthesis of lanthanum carbonate particles in presence of malic
acid (MA)
La(NO3)3, urea and different amounts of MA (Figure 32)
were dissolved in water. The solution of MA was
neutralized with NH3(aq) and the reaction mixture was
stirred and heated for 3 h in a flask reaction. The products
were precipitated and washed with ethanol or methanol
before drying. Two reactions (MA 12 and MA 15) were
performed without using any carbonate source.
The dried products were tested for their dispersibility in water. The products were
dissolvable in water yielding a clear solution when a clear solution had been obtained at the
end of the reaction. The solution was stable and the Tyndall effect could not be observed.
The products yielded a white, unstable suspension if a white suspension was obtained after
Figure 33: XRD-spectra of MA 2 (4 mmol MA), MA 12 (8 mmol MA), MA 13 (8 mmol MA) and MA 14 (1 mmol MA)
Figure 32: malic acid (MA)
62
the reaction was stopped. The stability of the suspension is more or less comparable with the
stability of uncoated nanoparticles in suspension. The recorded XRD-spectra (Figure 33)
indicate that all samples are amorphous. No peaks characteristic for lanthanum carbonate or
lanthanum hydroxycarbonate can be distinguished and all the spectra are very similar.
Elemental analysis (Table 10) shows that there is little difference between the amount of
carbon in MA 13 (8 mmol MA) and MA 12 (sample with no carbonate source added, 8 mmol
MA). This indicates that very little additional carbon is built in when using a carbonate
source. For MA 2 (4 mmol MA) and MA 15 (sample with no carbonate source added, 4 mmol
MA) we see that the amount of carbon is considerably lower, but this can be explained by the
fact that smaller amounts of malic acid were used. The nitrogen is assumed to originate from
the lanthanum source, the NH3(aq)- solution used to neutralize the malic acid solution or from
the decomposition products of urea. Like stated in the previous chapter the lanthanum
source probably does not have a lot of influence.
Table 10: elemental analysis of the obtained products synthesized in the presence of malic acid
MA 2 MA 12 MA 13 MA 15
Nitrogen (%) 0,45 3,70 8,77 0,40
Carbon (%) 18,73 23,42 24,26 17,55
Hydrogen (%) 3,27 4,32 5,31 2,77
In the case of MA 13 no core/shell nanoparticles were formed. Most likely a water soluble
complex between malic acid and lanthanum is formed. No particles were visualized taking a
TEM picture of MA 13. Also the Tyndall effect could not be observed, which would be a clear
indication for the formation of particles. The precise composition of the formed products
could not be determined. It could be that, alike to AEP, malic acid is too strong a ligand and
the carbonate ions cannot compete with it. A TEM picture of MA 2 (Figure 34) does show
that particles are formed although the XRD pattern does not give any indication for this.
Other examples of poorly corresponding XRD spectra can be found in literature. [3, 33, 69-
71] Comparing the elemental analysis of MA 2 and MA 15 (no carbonate source used) shows
63
that additional carbon is built in when a carbonate source is used, but the difference is small.
It could be that carbonates are formed, but only in small amounts.
A DRIFTS spectrum of MA 2 is recorded (Figure 35), which matches the spectrum of ZL 18
quite closely. The strong peak at 3600 cm-1 is not visible which indicates that most likely no
hydroxy carbonates are formed. The peaks around 500 cm-1 are less obvious. No CO2 or
presence of malic acid are observed in the DRIFTS spectrum. MA could act as a capping
agent, but from the TEM picture one can see that malic acid does not influence the size nor
the shape of the particles in any significant way. The particles are very large (in the order of
μm) and aggregated. The fact that carbonate particles are formed in this case can be
explained by the fact that less malic acid is present so there is less competition for the
carbonate ions to bind to the lanthanum ion. It could be that the ligand is too small to
influence the shape of the carbonate particles. No improvement in solubility was obtained
for these particles. Most likely this is due to the size of the particles. The unclear XRDs can be
a consequence of amorphous lanthanum carbonate.
Figure 34: TEM picture of MA 2
64
Figure 35: DRIFTS spectrum ZL 18 and MA 2
65
7 Synthesis of lanthanum carbonate particles in presence of glucose
(Gluc)
La(NO3)3, varying amounts of glucose (Figure 36)
and urea were dissolved and mixed together. A
flask reaction was performed. In addition a
reaction without urea (Gluc 10) was carried out.
Depending on the reaction a clear or white
suspension was obtained. In the case of a white
suspension the product was washed with
methanol or ethanol. A white powder was
obtained. In the case of a clear suspension the
products were precipitated by increasing the pH and purified by redissolving and then
precipitating them again. The precipitates were dried under vacuum and a dark yellow-
brown powder was collected.
Figure 36: D-glucose (left) α-D-glucose (right)
Figure 37: XRD of Gluc 2
66
The redispersibility of the white powders, Gluc 2 (4 mmol glucose) and Gluc 3 (8 mmol
glucose), is comparable with the solubility of the uncoated lanthanum carbonate
nanoparticles. No visual improvement of stability was observed. Gluc 12 (12 mmol glucose)
on the other hand was not soluble in water anymore after drying, while Gluc 10 was water
soluble after drying. Both powders gave the impression that the glucose present
decomposed during the drying process. Elemental analysis (Table 11) demonstrates that no
nitrogen has built into in the particles.
The XRD spectrum of Gluc 2 (Figure 37) shows that La2O(CO3)2·1,4 H2O has been formed. [72]
The XRD pattern of Gluc 3 was the same as Gluc 2. Elemental analysis results agree quite
close with the predicted values for the percentage of carbon, but there is more hydrogen
present than expected. This can also be a consequence of adsorbed water at the surface of
the particles. Infrared measurements (Figure 38) confirm that no hydroxyl carbonates are
formed. The spectra are similar with the LaOHCO3 spectra recorded for the uncoated
nanoparticles. Only the OH vibration around 3600 cm-1 originating from the OH group in
LaOHCO3 is absent. The peak slightly over 1000 cm-1 can be ascribed to the ν1 mode of the
carbonate ions. The peaks around 1500 cm-1 are assigned to the ν3 mode . Also water (3500
cm-1) and CO2 (2500 cm-1) is observed.
Figure 38: DRIFTS spectrum Gluc 2
67
TEM and SEM images revealed a very interesting observation (Figure 39). One can see that
the presence of glucose drastically influences the shape of the particles. Rod-shaped particles
are formed. They are still quite large, about 200 nm in diameter and several 100 nm long.
Infrared measurements show no evidence that glucose is bound to the surface of the rods. It
might be that glucose only serves as a chelating agent during the synthesis and so influences
the shape and morphology of the particles. Increasing the amount of glucose also gave rod-
shaped particles, however more aggregated. The rods organize in oval-shaped chunks. Also
smaller particles, which seemed to have only started to grow could be observed.
Jeevanandam et al. obtained La2O(CO3)2·1,4 H2O particles with a similar morphology via
sonochemical synthesis without the presence of any stabilizing ligand. [72]
In the case of Gluc 12 a clear solution was obtained before precipitating the particles, but the
Tyndall effect was not observed. The particles could be precipitated and resuspended before
the drying process. Drying seems to have an adverse effect. Yet TEM analysis shows the
formation of particles in the case of Gluc 12. The TEM images were taken before drying the
products. So a drop of the clear solution obtained after purifying was placed on the grid and
the water was allowed to evaporate. One can see a mixture of rod-shaped particles and also
cube-shaped particles. Cube shaped particles were also described in the report of Shan et al
[53] where a fluoride core is used. The cube-shaped particles are very big. In general one can
see a mixture of bigger and smaller particles. There is however a very small amount of
particles present on the grid. Elemental analysis (Table 11) indicates that additional carbon is
built in when a carbonate source is used. Also XRD analysis shows the difference between
Gluc 10 (no carbonate source) and Gluc 12 (Figure 40). Gluc 10 is rather amorphous and no
Figure 39: TEM picture of single rods (left) and SEM picture of more aggregated rods (right)
68
distinct peaks can be distinguished. In Gluc 12 a few distinct peaks can be seen, but
unfortunately these could not be assigned.
Table 11: elemental analysis of the obtained products synthesized in the presence of glucose
Also DIRFTS measurements were conducted, but these did not help determining the
composition of the formed products. Glucose has a lot of peaks in the region where the
characteristic peaks for carbonate ions appear. This makes it difficult to distinguish the
difference. The measurements did reveal that no hydroxycarbonates were formed since the
characteristic peak around 3600 cm-1 for the OH-group of LaCO3OH is absent.
Although there is a big difference in the amount of carbon between Gluc 10 and Gluc 12, no
clear evidence can be found that lanthanum carbonate has formed. In Gluc 12 particles were
observed under the TEM, but it was not possible to determine the exact composition of
these particles. There was only a very small amount of particles present. This could suggest
that the particles are only a byproduct and that mainly complexes are formed. The amount of
particles could be so small that the Tyndall effect is not observed. One should also take into
consideration that during the drying process decomposition of the products could have taken
place.
Gluc 2 Gluc 10 Gluc 12 Predicted values for La2O(CO3)2·1,4 H2O
Carbon (%) 5,87 5,08 10,29 5,47
Hydrogen (%) 1,29 4,33 3,60 0,64
69
Figure 40: XRD of Gluc 10 and Gluc 12
Repeating reaction Gluc 2 with La(OAc)3 as lanthanum source yielded a clear solution. The
Tyndall effect could not be observed and the XRD was the same as the XRD of Gluc 12. In
contrary this product was water soluble after drying. Small particles were observed under the
TEM. These particles were not uniform and very aggregated.
70
8 LnF3/glucose core/shell nanoparticles
A modified synthesis method of Shan et al. [53] was used. Glucose was dissolved in water
and while stirring NaF was added. The reaction mixture was heated to 60 °C and the
lanthanum source, La(NO3)3, was added. After 1,5 h (Gluc 6) or 3 h (Gluc 17) a clear solution
was obtained as a result of the reaction. The particles were precipitated by increasing the pH.
A procedure of precipitating and resuspending the particles was used to purify the products.
Finally the products were collected by centrifuge and dried. A pale yellow powder was
obtained. The exact synthesis as in the article was also carried out (Gluc 13).
After drying the powders were perfectly resuspendable in water. The Tyndall effect could be
observed. The formed phase was determined using XRD (Figure 41). The XRD pattern agrees
with the pattern of LaF3 presented in the article. In fact some of the peaks in the XRD
spectrum of Gluc 17 are more distinct then in the XRD published in the article. There is quite
some noise in the background, but this can be due to the coating of the particles with
glucose.
Figure 41: XRD of glucose coated LaF3 nanoparticles
71
TEM images of the samples were taken. The particles obtained by repeating the synthesis
procedure used in the article (Gluc 13) were small, but quite agglomerated. The cubic form
was not observed. The particles obtained in reaction Gluc 17 (Figure 42) were small (about 10
nm) and less aggregated. They appear however to pack closely on the TEM grid. Also in the
case of Gluc 6 small particles could be seen. No cubic particles were observed in any of the
samples.
Elemental analysis (Table 12) indicates that only a negligible amount of nitrogen has built in.
Carbon and hydrogen are present in the sample, assumable originating from the glucose.
From the elemental analysis it is estimated that the sample consist of about 14,5 % glucose.
Infrared measurements were performed (Figure 43). In literature IR spectra of LaF3 can be
found, but only bands indicating the presence of water or the used ligand could be seen in
the spectra. [54, 73] In this case we expected to see bands that corresponded with the bands
of glucose. Clearly there are some matching bands. Gluc 17 however seems to have shaper
peaks and more fine structure. The additional peak around 1750 cm-1 in the spectrum of Gluc
17 can be due to νC=O from glucose in the acyclic form.
Table 12: elemental analysis of Gluc 17
Gluc 17
Nitrogen (%) 0,01
Carbon (%) 2,75
Hydrogen (%) 0,76
Figure 42: TEM image of Gluc 17
72
It can be stated that glucose coated LaF3 core/shell nanoparticles were formed. When
repeating the reaction clear solutions were obtained and it was proven by XRD that LaF3 had
formed. Unfortunately TEM measurements were not as good as previously. One could still
see that small particles had formed, but they were imbedded in a film. Further research
should be carried out to investigate this subject.
Figure 43: DRIFTS spectrum of Gluc 17 and glucose
Replacing La(NO3)3 with Y(NO3)3 (Gluc 15), Gd(NO3)3 (Gluc 16) or La(OAc)3 (Gluc 24) yielded
white suspensions. The products were washed with EtOH or MeOH before drying.
XRD measurements (Figure 44) show that in the case of La(OAc)3 as lanthanum source LaF3
was formed. YF3 was formed when Y(NO3)3 was used [74]. The reaction where Gd(NO3)3 was
used yielded a rather amorphous product, so it is difficult to distinguish the GdF3 XRD-
pattern. [47]
73
Figure 44: XRD patterns of Gluc 24 (LaF3), Gluc 15 (YF3) and Gluc 16 (GdF3)
In each case the products were resuspendable in water yielding a white suspension which
was rather stable. In the case of Gluc 24 a long sonification time (± 15 min) was needed
before the product resuspended. TEM measurements showed that no nanoparticles had
formed, likely only the bulk material. In the case of Gluc 15 and Gluc 16 rod-like fiber bundles
were formed (Figure 45). The rods are about 500 nm long. Altough the fibers aggregate into
rods, the rods themselves are not very aggregated. As with glucose and lanthanum carbonate
also in this case this morphology for YF3 particles was obtained previously via a sonochemical
reaction without the presence of any stabilizing ligand. [74]
74
Figure 45: TEM picture (left) and SEM picture (right) of Gluc 15
75
9 General conclusion
The ultimate aim of this project was to synthesize core/shell nanoparticles with an inorganic
core consisting of lanthanum carbonate. Several ligands have been selected, but up to date
no core/shell nanoparticles of this form have been synthesized. In the case of AEP no
particles were formed. Probably a water soluble complex was formed, but the exact
composition of the formed products could not be determined. In the case of malic acid
particles were formed when small amounts of the ligand were used. It is suspected that
these particles only form as a byproduct. Malic acid did not seem to influence the size or
morphology of the particles. When higher amounts of the ligand were used, no particles
were visualized. Most likely, as with AEP, a water soluble complex is formed. Glucose as a
chelating agent had an interesting effect on the morphology giving rod shaped particles. XRD
showed that La2O(CO3)2·1,4 H2O had formed. Increasing the amount of glucose had a
negative effect on the uniformity of the particles. Additionally they showed a higher
tendency to aggregate. It may be concluded that lanthanum carbonate is not suited as an
inorganic core for core/shell nanoparticles.
Satisfying results were obtained synthesizing lanthanum hydroxycarbonate nanoparticles.
Especially small particles were obtained with La(OAc)3 as lanthanum source, although the
dispersibility in water was poor. Selected samples of the lanthanum hydroxycarbonate
particles were chosen and doped with Eu3+ and Tb3+, which are highly luminescent. Lifetimes
of about 1,6 ms for Tb3+ and about 600 μs for Eu3+ in solid state were obtained.
Core/shell nanoparticles were obtained with a lanthanum fluoride core. The synthesis
method of Shan et al. [53] was modified. Unfortunately TEM measurements were not always
very good. Replacing the lanthanide source with Y(NO3)3 or Gd(NO3)3 gave interesting results
regarding the morphology of the particles.
76
10 References
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11 Appendix
11.1 Synthesis methods
11.1.1 Synthesis of lanthanum carbonate nanoparticles
11.1.1.1 Uncoated lanthanum carbonate particles
For synthesizing uncoated lanthanum carbonate nanoparticles hydrothermal conditions were
used. The reactions were carried out at different temperatures and times. La(NO3)3 was used
as lanthanum source, but different amounts of water and different carbonate sources (urea
and Na2CO3) were investigated. As a result of the reactions white powders were formed
which were washed with methanol or ethanol and collected by centrifuging. The products
were dried in the oven (60°C). The different syntheses are summarized in Table 13.
Table 13: synthesis of the uncoated lanthanum carbonate particles with La(NO3)3 as a lanthanum source
Sample Amount of
La(NO3)3
(mmol)
Amount of
Na2CO3
(mmol)
Amount of
urea
(mmol)
Amount of
water (ml)
Time
(h)
Reaction
temperature
(°C)
ZL 16 3 3 - 50 12 120
ZL 32 3 3 - 50 12 140
ZL 34 3 3 - 50 24 120
ZL 18 1,5 - 15 20 24 120
ZL 26 1,5 - 15 20 12 140
ZL 29 1,5 - 15 20 24 140
ZL 20 1,5 - 15 30 24 120
ZL 27 1,5 - 15 30 12 140
ZL 30 1,5 - 15 30 24 140
ZL 21 1,5 - 15 50 24 120
ZL 28 1,5 - 15 50 12 140
ZL 31 1,5 - 15 50 24 140
81
In addition La(OAc)3 was used as lanthanum source. The reaction was carried out in water
with urea or Na2CO3 as carbonate source. The reaction time was 24 h and the temperature
was set to 120 °C. The exact parameters can be found in Table 14. Purification occurred the
same way as described above.
Table 14: synthesis of the uncoated lanthanum carbonate particles with La(OAc)3 as a lanthanum source
Sample Amount of
La(OAc)3
(mmol)
Amount of
Na2CO3
(mmol)
Amount of
urea
(mmol)
Amount of
water (ml)
Time (h) Reaction
temperature
(°C)
ZL 19 1,5 - 15 20 24 120
ZL 33 3 3 - 50 24 120
ZL 47 1,5 - 15 20 12 120
Finally a reaction with water and ethanol as a solvent was performed (ZL 24). 3 mmol of
La(NO3)3 were used together with 30 mmol of urea. The hydrothermal reaction was carried
out at 160 °C for 24 h in 12,5 ml of ethanol and 12,5 ml of water. Purification was done in the
same way as described before.
The reaction conditions of ZL 18 and ZL 28 were chosen for doping the particles with
Eu(NO3)3 or Tb(NO3)3. The specific details are summarized in Table 15
82
Table 15: doping percentages of the synthesized particles
Eu3+(%) Tb3+(%) Time (h) Temperature (°C)
ZL 35 - 5 12 140
ZL 36 - 2 12 140
ZL 40 - 0,1 12 140
ZL 41 - 1 12 140
ZL42 - 10 12 140
ZL 49 - 2 24 120
ZL 50 - 5 24 120
ZL 51 - 10 24 120
ZL 52 - 12 24 120
ZL 53 - 15 24 120
ZL 54 - 20 24 120
ZL 55 2 - 24 120
ZL 56 5 - 24 120
ZL 57 10 - 24 120
ZL 58 12 - 24 120
ZL 59 15 - 24 120
ZL 60 15 - 24 120
11.1.1.2 Using 2-aminoethyl phosphate (AEP) as a ligand
During the synthesis procedure 1,5 mmol of La(NO3)3 and 4 mmol of AEP were used. Na2CO3
and urea were used as carbonate source. Each substance was dissolved separately and in
total 30 ml of water was used. The AEP-solution was neutralized with NH3(aq). First the
lanthanide solution was added to the solution of the ligand and the carbonate source was
added last to the reaction mixture. The flask reaction was carried out at 85 °C for 2 or 3
hours. The specific details are summarized in
Table 16. In each case clear solutions were obtained. A synthesis without any carbonate
source was carried out following the same procedure as described above, only in this case 20
83
ml of water was used in total. The reaction gave a white suspension. The products were
precipitated and washed with ethanol or methanol. They were collected by centrifugation
and dried in the oven (60 °C). In each case a white powder was acquired.
Table 16: synthesis of lanthanum carbonate in presence of AEP
Sample Amount
of
La(NO3)3
(mmol)
Amount
of AEP
(mmol)
Amount
of water
(ml)
Amount
of
Na2CO3
(mmol)
Amount
of Urea
(mmol)
Time (h) Color of
the
solution
after
reaction
AEP 11 1,5 4 30 1,5 - 2 clear
AEP 17 1,5 4 30 1,5 - 3 Clear/pale
white
AEP 19 1,5 4 30 - 15 3 clear
AEP 20 1,5 4 30 - - 2 white
11.1.1.3 Using malic acid (MA) as a ligand
For each reaction 1,5 mmol of La(NO3)3 was used together with 15 mmol of urea. The
amounts of malic acid varied (Table 17). Each substance was dissolved separately and in total
50 ml of water was used. The solution of malic acid was neutralized with NH3(aq). The
reactants were added in the following order: malic acid solution, lanthanum solution and
finally the urea solution. The reaction was a flask reaction, stirred at 80 °C for 3 hours. In the
case of MA 12 and MA 15 no urea was used. Depending on the amount of MA used the
reactions gave a clear or white suspension (Table 17). The products were precipitated and
washed with ethanol or methanol. In the case of a white solution the products could be dried
in a normal oven (60 °C) otherwise the vacuum oven was used. White powders were
obtained.
84
Table 17: synthesis of lanthanum carbonate in presence of malic acid
Sample Amount of
La(NO3)3
(mmol)
Amount of MA
(mmol)
Amount of
urea (mmol)
Amount of
water (ml)
Color of the
solution after
reaction
MA 14 1,5 1 15 50 white
MA 2 1,5 4 15 50 white
MA 12 1,5 8 - 50 clear
MA 13 1,5 8 15 50 clear
MA 15 1,5 4 - 50 white
11.1.1.4 Using glucose (Gluc) as a ligand
1,5 mmol of La(NO3)3 was used together with varying amount of glucose (Table 18) and 15
mmol of urea. Each component was dissolved separately and the order of addition was the
following: glucose solution, lanthanide solution, urea solution. In total 50 ml of water was
used. The flask reaction was performed at 85 °C for 3 h. A reaction without urea (Gluc 10)
was additionally prepared. White or clear suspensions were obtained. In the case of a white
suspension the product could be collected by centrifuging, it was washed with methanol or
ethanol and dried in the oven (60°C). In this case white powders were gained. In the case of a
clear solution the products were precipitated by increasing the pH using a NaOH solution and
centrifuging. They could be redissolved by adjusting the pH to 7-6 by adding a HCl solution.
This was done multiple times in order to purify the products. The precipitates were dried
under vacuum and (slightly) yellow products were obtained.
85
Table 18: synthesis of lanthanum carbonate in presence of glucose
Sample Amount of
La(NO3)3
(mmol)
Amount of
urea (mmol)
Amount of
water (ml)
Amount of
glucose
(mmol)
Color of the
solution after
reaction
Gluc 2 1,5 15 50 4 white
Gluc 3 1,5 15 50 8 white
Gluc 12 1,5 15 50 12 clear
Gluc 10 1,5 - 50 12 clear
In Gluc 23 La(OAc)3 was used as lanthanum source under the same reaction conditions as
Gluc 2: 1,5 mmol La(OAc)3, 15 mmol urea, 4 mmol glucose and 50 ml of water in a flask
reaction at 85 °C for 3 hours. A clear solution was obtained. Purification was performed as
described above for clear solutions.
11.1.2 Glucose coated fluoride nanoparticles
A modified synthesis method of Shan et al. [53] was used. 2 g of glucose was dissolved in 20
ml of water and while stirring 0,156 g of NaF was added. The stirred reaction mixture was
heated to 60 °C after which 0,65720 g of La(NO3)3 dissolved in 3 ml of water, was added. The
flask reaction was stirred for 1,5 or 3 h at 60 °C. After the reaction was stopped a clear
suspension was obtained. The particles were precipitated by increasing the pH above 7 using
a NaOH solution. The precipitate could be redissolved using a HCl solution. The procedure of
precipitating and redissolving was repeated several times with the objective to purify the
products. Finally the products were collected by centrifuge and they could be dried in the
oven (60 °C). A pale yellow powder was obtained. An unmodified synthesis (described in the
article) was additionally carried out for comparison (Gluc 13). Everything is summarized in
Table 19.
86
Table 19: synthesis of glucose coated LaF3 nanoparticles
Sample Amount of
La(NO3)3 (g)
Amount of NaF
(g)
Amount of
glucose (g)
Reaction time (h)
Gluc 6 0,65720 0,156 2 1,5
Gluc 13 0,65720 0,156 2 ± 120
Gluc 17 0,65720 0,156 2 3
Reaction Gluc 6 was repeated with Y(NO3)3 (Gluc 15), Gd(NO3)3 (Gluc 16) and La(OAc)3 (Gluc
24) as lanthanide source. White suspensions were obtained. The products were collected by
centrifuge and washed with EtOH or MeOH before drying.
87
11.2 Luminescence spectra
In this section the remaining emission spectra of the lanthanum carbonate samples can be
found.
88
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90
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92
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94
95
96
97
98
99
100
101
