7. Luminescent Materials€¦ · Chapter Luminescent Materials Slide 6 Incoherent Light Sources...

Chapter Luminescent Materials

Slide 1

Incoherent Light Sources

Prof. Dr. T. Jüstel

7. Luminescent Materials

Content

7.1 History

7.2 Definition and Working Principle

7.3 Luminescence Mechanisms

7.4 Chemical Composition

7.5 Composition and Function

7.6 Application Areas

7.7 Broadband Phosphors

7.8 Line Phosphors

7.9 UV-A Phosphors

7.10 UV-B Phosphors

7.11 UV-C Phosphors

7.12 IR-A Phosphors

7.13 Future Trends

Cd(S,Se) Quantum dots


Slide 2



7.1 History

Some milestones

• Stone of Bologna: Barit (Galilei 1600)

• Discovery of phosphors (phosphorescence) (Brand 1669)

• First phosphor by reaction of shells with sulfur (Canton 1768)

• Application of a phosphor in combination with a Hg-discharge (Becquerel 1859)

• Patent on the use of CaWO4 in fluorescent lamps (Edison 1896)

• Fluorescent lamps with MgWO4 + (Zn,Be)2SiO4:Mn (GE 1938)

• Development of Ca5(PO4)3(F,Cl):Sb,Mn (McKeag 1942)

• ZnS:Ag, (Zn,Be)2SiO4:Mn and Zn3(PO4)2:Mn for first color CRT (1958)

• Fluorescent lamps with Eu- and Tb- phosphors (Verstegen 1974)

• First oxidic afterglow pigment SrAl2O4:Eu,Dy (Nemoto 1993)

• Nitride phosphors (Schnick 1995)

• K2SiF6:Mn4+ as red line emitter for LEDs (GE 2006)

• Transparent ceramics converter for LEDs (Philips 2007)

• Narrow band red nitride phosphor Sr[LiAl3N4]:Eu (Schnick 2014)


Slide 3




Definition

A phosphor is a micro-or nanoscale pigment, that after excitation by radiation

(NIR-,VIS-, UV-, X-ray-, gamma-), high-energy particles or matter vibrations

(phonons), emits electromagnetic radiation beyond thermal equilibrium.

Upon excitation by electrons or UV radiation

Under daylight


Slide 4




Working principle

1. Excitation: Absorption of energy from an external source

2. Energy transfer: To activator ions (luminescence) or defects (storage)

3. Relaxation : Radiative: Emission (luminescence) → Luminescent pigm.

Non-radiative: Heat (phonons) → Pigment

SEM image of (Y,Gd)BO3:Eu

Typical particle size 1 - 10 µm

Excitation

SourceEmission

HeatHeat

SET

D

Emission

A

A A

Heat

Heat

ETET

ET

Heat


Slide 5



7.3 Luminescence MechanismsType Physical process (time scale)

Fluorescence Spin-allowed transition (ns - µs)

Phosphorescence Spin-forbidden transition (ms)

Afterglow (pers. luminescence) Thermal activation of charge carriers (s)

Type Excitation source Applications

Photoluminescence UV photons Fluorescent lamps

X-rays luminescence X-rays X-rays intensifier

Cathodoluminescence Electrons TVs, monitors

Electroluminescence Electric field LEDs, EL displays

Thermoluminescence Heat Age determination

Chemiluminescence Chemical reaction Emergency signals

Bioluminescence Biochemical reaction Fireflies, jellyfish

Sonoluminescence Ultrasound -

Mechanoluminescence Mechanical energy -


Slide 6



Organic phosphors

Requirements and properties

• usually aromatic compounds (no C-H, N-H, or O-H bonds, since > 2900 cm-1)

• low energy p → p * transitions

• quantum yield increases with number of rings and degree of condensation

• fluorescence especially favored for rigid structures

• fluorescence increase for bounding to a metal → complex formation

Examples of selected fluorescent compounds

Perylenes [Al(8-hydroxyquinolinate)3 [Ir(phenylpyridine)3]


N N

O

O

O

O

O O

OO


Slide 7



Inorganic phosphors (Luminescent pigments)

• Host material + Dopants + Defects

• Dopants = Activators + Sensitizers + Impurities

• Defects = 0-D (vacancies), 1-D (dislocations), 2-D (boundaries, surfaces), 3-D (pores)

Example: La1-x-yCexTby(PO4) = (La,Ce,Tb)PO4 = LaPO4:Ce,Tb = Ce,Tb:LaPO4



Slide 8




Composition Inorganic host + Dopants + Impurities + Defects

Dopants = Activator/Sensitizers (Impurities) = RE-, TM-, and s2-ions

La57

Y39

Sc21

Hf72

Zr40

Ti22

Ta73

Nb41

V23

W74

Mo42

Cr24

Re75

Tc43

Mn25

Os76

Ru44

Fe26

Ir77

Rh45

Co27

Pt78

Pd46

Ni28

Au79

Ag47

Cu29

Hg80

Cd48

Zn30

Tl81

In49

Ga31

Al13

B5

Ba

Be4

Cs55

Rb37

K19

Na11

Li3

ZnH1

Pb82

Sn50

Ge32

Si14

C6

84

Te52

Se34

S16

O8

Bi83

Sb51

As33

P15

N7

At85

I53

Br35

Cl17

F9

Rn86

Xe54

Kr36

Ar18

Ne10

ZnHe2

Po

Ce58

Pr59

Nd60

Pm61

Sm62

Eu63

Gd64

Tb65

Dy66

Ho67

Er68

Tm69

Yb70

Lu71

Th90

Pa91

U92

Np93

Pu94

Am95

Cm96

Bk97

Cf98

Es99

Fm100

Md101

No102

Lr103

1

Ac89

RaFr87

2

3 4 5 6 7 8 9 10 11 12

13 14 15 16 17

18

1

2

3

4

5

6

7

Mg12

Ca20

Sr38

56

88

6

7

Rf104

Db105

Sg106

Bh107

Hs108

Mt109

Ds110

Rg111

Cn112


Slide 9



Luminescent pigment = Inorganic host + Dopants (Impurities) + Defects

Inorganic Host

• Selection in accordance to requirements defined by the application area:

Excitation energy, absorption strength, chemical environment, temperature, pressure and

so on

Dopants (Impurities)

• Selection and concentration depends on host lattice and application:

Solubility, mobility, oxidation state stability, CT state location

• Co-dopants to enhance absorption

Defects

• Afterglow (persistent luminescence)

• Luminescence quenching (conc. and temperature dependent)

• Stability reduction



Slide 10




Luminescent pigment = Inorganic host + Dopants (s2-, TM, or RE Ions) + Defects

Inorganic host

• Oxides Y2O3, Y3Al5O12, YBO3, YVO4, YPO4, LaPO4, BaMgAl10O17, …

• Sulfides ZnS, MgS, CaS, SrS, SrGa2S4, SrIn2S4, Y2O2S, Gd2O2S, …

• Fluorides CaF2, LiYF4, K2SiF6, KYF4, KY3F10, YOF, K2NbF7, …

• Nitrides CaSiN2, CaAlSiN3, Sr2Si5N8, La3Si6N11, SrSi2N2O2, SrLiAl3N4, …

Dopants (impurities)

• s2 Ions Sn2+, Sb3+, Tl+, Pb2+, Bi3+

• TM Ions Ti3+, V2+/3+, Cr3+/4+, Mn2+/4+, Fe3+, Co2+, Ni2+, Cu+/2+, Ag+, Au+

• RE ions Ce3+, Pr3+, Nd3+, Sm2+/3+, Eu2+/3+, Gd3+, Tb3+, Dy3+, Er3+, Tm3+, Yb2+/3+

Defects

• Cation vac. VC

• Anion vac. VA

• Interstitials I

• Colour cent. F


Slide 11



Luminescent pigment = Inorganic host + Dopants (impurities) + Defects

Inorganic Host• Coordination number and geometry• Symmetry of activator sites• Optical band gap• Phonon spectrum

Dopants (impurities) and defects• Concentration• Phase diagram and miscibility gaps

Particle surface• Zeta-potential• Surface area, surface energy• Coatings → Light in- and outcoupling

Particle morphology• Shape• Particle size distribution• Agglomeration


Eu2+

Eu2+

Eu2+

Mn2+

VO


Slide 12



Luminescent pigments – Particle Morphology and Surface Optimisation


Novel application areas lifetime, T1/2, ,

0.1 nm 1 nm 10 nm 100 nm 1 µm 10 µm 100 µm 1 mm 10 mm 100 mm

atoms cluster nano crystals micro crystals single crystals

amorphous matter nano ceramics ceramics (opaque)

super crystals ceramics (translucent)

core-shell particles ceramics (transparent)

Glasses CdSe, CsPbBr3 (Y,Tb,Lu)3Al5O12:Ce Lu3Al5O12:SE (SE = Ce - Yb)

(bio)marker, µ-LEDs, PV units high power LEDs/laser, scintillators, excimer lamps

ZnO:Zn

CdSe

BAM:EuYAG:Er

YBO3:Eu

0.001 0.01 0.1 1 10 100

0

5

10

15

20

25

30

d50= 5.9 µmd50= 0.1 µm

q [

%]

Particle Diameter [m]

0

20

40

60

80

100

Cu

mu

lative fraction

un

der size [vo

l-%]

d50= 0.005 µm


Slide 13




Most relevant physical properties

Photoluminescence

(PL) spectra

Absorption and

reflection spectra

Quantum yield (QY)

(internal and external)

Stability and colour

point consistency

Decay curves and

afterglow (T-dependent)

Thermal quenching

Linearity (saturation)

Temperature dependent PL of some

phosphors upon 254 nm excitation

250 300 350 400 450 500 550 600 650 700 750 800

0,0

0,2

0,4

0,6

0,8

1,0 PRO-2009-AB-012 ex307nm

PRO-2009-AB-012 mon656nm

Rela

tive

in

tensity [a.u

.]

Wavelength [nm]

656 nm

0 100 200 300 400 500

0,0

0,2

0,4

0,6

0,8

1,0 LiEuMo2O

8

Ideal

YAG:Ce U728

No

rm.

em

issio

n in

teg

rals

[a.u

]

Exc. density [W/mm2]

0 2000 4000 6000 8000 100001

10

100

1000

Decay Measurement

Inte

ns

ity

[c

ou

nts

]

time [ns]

T=100.00 K

T=150.00 K

T=200.00 K

T=250.00 K

T=300.00 K

T=350.00 K

T=400.00 K

T=450.00 K

T=500.00 K

Linearity of YAG:Ce

and LiEuMo2O8

PL (excitation and emission)

spectrum of Mg2TiO4:Mn

Decay curves of

SrSi2N2O2:Eu


Slide 14



Activator Host material Emission at [nm] Color Applications

Cr3+Al2O3 (Ruby)

Ga3Ga5O12 (Garnet)694

Red

IR-A

Solid State Laser

NIR LEDs

Mn2+Zn2SiO4 (Willemite)

BaMgAl10O17 (ß-Alumina)

525

515

Green

Green

PDPs, CRTs

PDPs, FLs

Mn4+Mg4GeO5.5F

K2SiF6

655

630

Deep Red

Red

Hg high-pressure lamps

LEDs

Fe3+ LiAlO2 735 Red FLs

Cu+ ZnS 530 Green CRTs

Ag+ ZnS 450 Blue CRTs

Sn2+ (Sr,Mg)3(PO4)2 630 Red Hg high-pressure lamps

Sb3+ (Sr,Ca)5(PO4)3(Cl,F) 480 Blue-Green FLs

Tl+ NaI

CsI

415

560

Blue

Yellow

x/-ray detectors

x/-ray detectors

Pb2+ BaSi2O5 (Sanbornite)

Sr2MgSi2O7 (Akermanite)

350

365

UV-A

UV-AFLs for tanning

Bi3+ Bi4Ge3O12 480 Blue-Green x/-ray detectors


Composition: Listed by the activator (transition metal ions and s2-ions)


Slide 15



Activator Host material Emission at (nm) Color Applications

Ce3+LaPO4

YPO4

Y3Al5O12 (Garnet)

320

335, 355

560

UV-B

UV-A

Yellow

FLs for tanning

FLs for tanning

FLs, LEDs

Pr3+Gd2O2S

CaTiO3

510

610

Green

Red

CT Scanner

FEDs

Nd3+ Y3Al5O12 (Garnet) 1064 IR-A Solid State Laser

Eu2+

SrB4O7

BaMgAl10O17

Sr4Al14O25

368

453

490

UV-A

Blue

Blue-green

FLs for tanning

FLs, PDPs

FLs

Eu3+Y2O3

YVO4

611

615

Red

Red

FLs

Hg high-pressure lamps

Gd3+ (La,Bi)B3O6 311 UV-B FLs for medical skin treat.

Tb3+LaPO4

CeMgAl11O19

(Gd,Ce)MgB5O10

544

544

544

Green

Green

Green

FLs

FLs

FLs

Yb3+ Y3Al5O12 (Garnet) 980 IR-A Solid State Laser


Composition: Listed by the activator (rare earth ions: Ce … Yb)


Slide 16




Application in Excitation source

Cathode ray tubes Electrons

X-rays intensifier X-rays

Plasma screens 147, 172 nm

Xe-discharge lamps 172 nm

Hg-high pressure discharge lamps 200 – 350 nm

Hg-low pressure discharge lamps 185, 254 nm

Emissive LCDs 370 – 400 nm

pcLEDs 370 – 480 nm

Main application areas: Lighting, imaging, and detection/sensing

Excita

tion

energ

y

Ho

st lattice A

ctiva

tor


Slide 17




TV

Fluorescent lamps

Plasma TVs

Electroluminescent

screens

LEDs

Tomography


Slide 18




Function Application field

Optical brighteners Paint, paper, clothing, detergent

Copy protection Banknotes, stamps, credit cards,

certificate, tickets

Product protection Pharmaceuticals, plastics

Security labeling Emergency exit lighting, emergency exits

Advertising / visualization Decoration, advertisememt, logos

Conversion of high-energy radiation or

particles

X-ray films, CTs, positron emission

tomography, EUV-amplifier

Cosmetics Dental ceramics, tanning lamps

Marker for the analysis Detection of nucleic acids + proteins

Lithographie Photocopier

Photochemistry and biology Water purification, disinfection, breeding

boxes and cabinets, air pollution control

Medicine Diagnostics, photodynamic therapy


Slide 19



7.7 Broadband Phosphors

Optical transitions

• Charge-Transfer

• 5s-5p, 6s-6p

• 4f-5d

• 3d-3d

Suitable activator ions/moieties

• VO43-, WO4

2-

• Sn2+, Sb3+, Tl+, Pb2+, Bi3+

• Ce3+, Eu2+, Yb2+

• Mn2+, Cr3+

Examples Mineral type

• (Zn,Be)2SiO4:Mn Willemite

• CaWO4 Scheelite

• MgWO4 Wolframite

• Ca5(PO4)3(F,Cl):Sb,Mn Apatite

FW

HM

300 350 400 450 500 550 600 650 700 750 8000,0

0,2

0,4

0,6

0,8

1,0 MgWO4

CaWO4

Em

issio

n in

ten

sity [a

.u.]

Wavelength [nm]


Slide 20



7.8 Line Phosphors

Optical transitions

• 4f-4f Sm3+, Eu3+, Tb3+, Er3+, Dy3+, Tm3+

• 3d-3d Mn4+, Cr3+

• Very weak electron-phonon coupling

• Lines or line multiplets

LaPO4:Tm

YBO3:TmY2O3:Eu

(Y,Gd)BO3:Eu

YVO4:Eu

LaPO4:Ce,Tb

LaMgB5O10;Ce,Tb

LaMgAl11O19:Ce,Tb

400 450 500 550 600 650 700 750 8000,0

0,2

0,4

0,6

Em

issio

n in

ten

sity [

a.u

.]

Wavelength [nm]

400 500 600 700 8000,0

0,2

0,4

0,6

0,8

1,0

Em

issio

n in

ten

sity [a

.u.]

Wavelength [nm]

400 500 600 700 8000,0

0,2

0,4

0,6

0,8

1,0

Em

issio

n in

ten

sity [a

.u.]

Wavelength [nm]


Slide 21



7.9 UV-A PhosphorsOptical transitions

• 4f-5d

• 6s-6p

Suitable activators

• Eu2+ (>365 nm)

• Ce3+

• Pb2+

Commercial materials Emission at Mineral type

• LaMgAl11O19:Ce 345 nm Magnetoplumbite

• YPO4:Ce 335, 355 nm Xenotime

• BaSi2O5:Pb 350 nm Sanbornit

• Sr2MgSi2O7:Pb 365 nm Akermanite

• SrB4O7:Eu 368 nm Borax

280 300 320 340 360 380 400 420 440 460

0,0

0,2

0,4

0,6

0,8

1,0

YPO4:Ce

LaMgAl11

O19

:Ce

Em

issio

n in

tensity [

a.u

.]

BaSi2O

5:Pb

SrB4O

7:Eu

Sr2MgSi

2O

7:Pb

Wavelength [nm]


Slide 22



7.10 UV-B Phosphors

Optical transitions

• 4f-5d

• 4f-4f

• 6s-6p

Suitable activators

• Ce3+

• Bi3+

• Gd3+ (311 nm)

Commercial materials Emission at Mineral type

• SrAl12O19:Ce 300 nm Magnetoplumbite

• LaB3O6:Bi,Gd 311 nm (Bi3+ → Gd3+ energy transfer)

• LaPO4:Ce 320 nm Monazite

260 280 300 320 340 360 380 400 420 440

0,0

0,2

0,4

0,6

0,8

1,0LaB

3O

6:Bi,Gd

Em

issio

n in

tensity [

a.u

.]

LaPO4:CeSrAl

12O

19:Ce

Wavelength [nm]


Slide 23



7.11 UV-C Phosphors

Optical transitions

• 4f-5d

• 6s-6p

Suitable activators

• Pr3+

• Bi3+

• Pb2+

Examples Emission at Mineral type

• YBO3:Pr 265 nm Vaterite

• YAlO3:Pr 245 nm Perovskite

• YPO4:Bi 240 nm Xenotime

• CaSO4:Pb 230 nm Anhydrite

200 250 300 350

0,0

0,2

0,4

0,6

0,8

1,0

YBO3:Pr

Em

issio

n in

ten

sity [

a.u

.]

CaSO4:Pb YPO

4:Bi

Wavelength [nm]


Slide 24



7.12 IR-A Phosphors

Optical transitions

• 3d-3d

• 4f-4f

Suitable activators

• Cr3+ 680 – 750 nm

• Fe3+ 700 – 800 nm

• Nd3+ ~ 1060 nm

• Yb3+ ~ 950 - 1050 nm

Examples Emission at Mineral type Application area

• Al2O3:Cr 694 nm Corundum Ruby laser

• LiAlO2:Fe 735 nm - Fluorescent lamps

• Y3Al5O12:Nd 1064 nm Garnet YAG:Nd laser

• Y3Al5O12:Yb 1028 nm Garnet YAG:Yb laser

200 400 600 800 1000 1200 1400 16000,0

0,2

0,4

0,6

0,8

1,0

Sample: Y3Al5O12:Nd

Rela

tive inte

nsity

Wavelength [nm]

Y3Al5O12:Nd


Slide 25



7.13 Future TrendsEfficiency: Light sources & displays

→ External quantum yield (EQY)

→ µ-particles → ceramics → single crystals

Lifetime: Light sources & displays

→ Defect density and particle coatings

Miniaturisation: µ-LED (displays)

→ PSD: Nanocrystals & Quantum Dots

→ Stability: Core-shell particles

Power density: HP LEDs & laser diodes

→ Decay time & ESA redox stability

→ Density of optical center 𝐍𝐚𝐜𝐭𝐢𝐯𝐚𝐭𝐨𝐫 [cm-3]

Novel spectra: NUV, NIR, human centric lighting

→ UV: (Al,Ga)N LED / Xe excimer lamps

→ NIR: (In,Ga)N LED + deep red/NIR emitter

EQ𝐘 =Number of emitted photon𝐬

Number of absorbed photon𝐬

ESA

CB

8S7/2

Eu2+: [Xe]4f7

(Eu2+)*: [Xe]4f65d1

En

erg

y

VB

𝐏𝐞𝐦,𝐦𝐚𝐱 = 𝐍𝐚𝐜𝐭𝐢𝐯𝐚𝐭𝐨𝐫𝐄𝐂𝐞𝐱𝐭𝐫𝐚𝐜𝐭𝐢𝐨𝐧 Τ𝐑 𝛕𝐫 (𝐑 = 𝐫𝐚𝐝𝐢𝐮𝐬)

Ref.: Brils Modell: A. Bril, Physica 15 (1949) 361

7. Luminescent Materials€¦ · Chapter Luminescent Materials Slide 6 Incoherent Light Sources...

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