Detection of defects in minerals by luminescence spectroscopy · Luminescence of inorganic and...

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Sm3+

Eu2+

Sm3+

Nd3+

Dy3+

Detection of defects in minerals by

luminescence spectroscopy

Detection of Detection of defects defects in in minerals by minerals by

luminescence spectroscopyluminescence spectroscopyJens Götze

TU Bergakademie Freiberg

1. Physical basics of luminescence phenomena

2. Defects in minerals and the luminescence signal

3. Factors influencing the luminescence properties of minerals- typomorphic properties (quartz)- crystal chemistry (feldspar minerals)- aspects of quantitative luminescence spectroscopy

4. Conclusions

ContentContent

Physical basics of luminescence phenomena

Physical basics of luminescence phenomena

???

LuminescenceLuminescence

= transformation of diverse kinds of energyinto visible light

Basics of luminescence

Luminescence of inorganic and organic substances

results from an emission transition of anions, molecules

or a crystal from an excited electronic state to a ground

state with lesser energy.

(Marfunin1979)


Main processes of luminescence

(1) absorption of excitation energy and stimulationof the system into an excited state

(2) transformation and transfer of the excitation energy

(3) emission of light and relaxation of the systeminto an unexcited condition

Schematic model of luminescence processes

Excitationby energy

Emissionof light

e-

biological processes bioluminescence

thermal excitation

electrons

UV photoluminescence

thermoluminescence

cathodoluminescence


The band modelThe band model


valence band

conduction band

insulatorconductor semiconductor

E

Energy levels in a band scheme for different crystal types

band gap

band gap

insulator

E (photonenergy)


Valence band

E

luminescence

(a) (b) (c)

activator

trap

(d)

Conduction band21


intrinsic luminescence

radiatio nlesstransition

extrinsic luminescence

The configurational coordinatemodel

The configurational coordinatemodel



excitedstate

groundstate

Configurational coordinate diagram for transitions according to the Franck-Condonprinciple with related absorption and emission bands, respectively.(modified after Yacobi & Holt 1990)

absorptionband

emissionband


Excitation (1) and emission (2) spectra of Mn2+ in calcite (after Medlin 1964)

1

2

Stokes shift

???

Defects in minerals and theluminescence signal

Defects in minerals and theluminescence signal

(2) Luminescence spectroscopy(1) Luminescence microscopy

contrasting of different phases

visualization of defects, zoningand internal structures of solids

oapatite

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Sm3+

Eu2+

Sm3+

Nd3+

Dy3+

determination of the real structure

detection of defects, trace elementstheir valence and structural position

Detection of the „real structure“ (defect structure)

cc

Importance of spatially resolved analyses !

Defects in minerals and the luminescence signal

Luminescence centres

transition metal ions (e.g., Mn2+, Cr3+, Fe3+)

rare earth elements (REE2+/3+)

actinides (especially uranyl UO22+)

heavy metals (e.g., Pb2+, Tl+)

electron-hole centres (e.g., S2-, O2

-, F-centres)

crystallophosphores of the ZnS type (semiconductor)

more extended defects (dislocations, clusters, etc.)

extrinsic

intrinsic pure lattice defects(broken bonds, vacancies)

trace elements(Mn2+, REE2+/3+, etc.)


activator

ligands

The crystal field theoryThe crystal field theory

Factors of the crystal field influence(crystal field splitting ∆ or 10Dq):

- type of the activator ion (size, charge, electron configuration)

- type of the ligands

- the interaction distance

- local symmetry of the ligand environment, etc.

(Burns, 1993)

the stronger the interaction of the activator ion with the lattice,the greater are the Stokes shift and the width of the emission line

local environment of the activator ion


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zircon

Dy3+

Dy3+

Dy3+

Dy3+

zircon

scheelite

anhydrite

calcite

fluorite

apatite400 500 600 700 [nm]

Dy3+

Tb3+

Dy3+ Sm3+Dy3+

Sm3+

Sm3+

Sm3+

Tm3+

Influence of the crystal field on luminescence emission spectraInfluence of the crystal field on luminescence emission spectra

(1) influence of the crystal field = weak

CL emission spectra are specificof the activator ion

CL spectra of narrow emissionlines (e.g. REE3+)



(2) influence of the crystal field = strong

CL emission spectra are specificof the host crystal

CL spectra of broad emissionbands (e.g. Mn2+, Fe3+)

Mn2+calcite

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Mn2+ activated CL of CaCO3:

aragonite green (~560 nm)

calcite yellow-orange (~610 nm)

magnesite red (~655 nm)


plagioclase

Fe3+Mn2+

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]0 20 40 60 80 100

An content [mol-%]

Position of the Fe3+ activated CL emission band in plagioclases in relation to theanorthite content

IRredlunar plagioclases



Factors influencing the luminescence properties of minerals


Mineral groups and minerals showing CLMineral groups and minerals showing CL

in general all insulators and semiconductors

elements diamondsulfides sphaleriteoxides corundum, cassiterite, periclasehalides fluorite, halitesulfates anhydrite, alunitephosphates apatitecarbonates calcite, aragonite, dolomite, magnesitesilicates feldspar, quartz, zircon, kaolinite

technical products (synthetic minerals, ceramics, glasses !)

Minerals show characteristic luminescence properties in dependence on their specific conditions of formation.


1. Typomorphic properties1. Typomorphic properties

close relationship between specific conditions of quartz formation, real structure and luminescence properties of quartz may provide important genetic information

Quartz (SiO2)Quartz (SiO2)

Real structure of quartzReal structure of quartz

one-dimensional point defects(1) defects of trace elements(2) pure lattice defects

dislocations (two-dimensional)

three-dimensional fluid andmineral inclusions

defects in thecrystal structure

„fingerprints“ of theformation history

SiO4-tetrahedra

OO O

O

Si

Detection of defects by Electron Spin Resonance (ESR)Luminescence Spectroscopy

Real structure of quartzReal structure of quartz

Paramagnetic defects in quartzParamagnetic defects in quartz

(Plötze 1995)

Characteristic CL emission bands in quartz (modified after Götze et al. 2001)Characteristic CL emission bands in quartz (modified after Götze et al. 2001)

Emission Suggested activator References

175 nm (7.3 eV) intrinsic emission of pure SiO2 Entzian & Ahlgrimm (1983)

290 nm (4.28 eV) oxygen vacancy Jones & Embree (1976)

330-340 nm oxygen vacancy Rink et al (1993)(3.75-3.6 eV) [AlO4/Li+] centre Demars et al. (1996)

[TiO4/Li+] centre Plötze & Wolf (1996)

380-390 nm [AlO4/M+] centre; M+= Li+, Na+, H+ Alonso et al. (1983)(3.2-3.1 eV) [H3O4]0 hole centre Young & McKeever (1990)

450 nm (2.8 eV) self-trapped exciton (STE) Stevens Kalceff & Phillips (1995)

470-500 nm extrinsic emission Itoh et al. (1988)(2.6-2.45 nm) [AlO4 /M+]0, GeO4/M+]0 centres McKeever (1984), Götze et al. (2004)

580 nm (2.1 eV) E‘ centre (oxygen vacancy) Rink et al. (1993); Götze et al. 1999)

620-650 nm nonbridging oxygen hole centre (NBOHC) Siegel & Marrone (1981)(1.97-1.9 eV) with several precursors Stevens Kalceff & Phillips (1995)

705 nm (1.7 eV) substitutional Fe3+ Pott & McNicol (1971)

visi

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UV

Quartz from rhyolite, Thunder Bay (Canada)

450 nm and 650 nm CL emission bands450 nm and 650 nm CL emission bands

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300 µm

most common CL emissions in igneous quartz

Rochlitz 400 µm

Radiation halos in quartz grains of the U/Au deposit Witwatersrand, RSA

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Witwatersrand

blue core

violet

orangerim

300 µm













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Quartz from pegmatite, Brattekleiv (Norway)

500 nm CL emission band (transient CL)500 nm CL emission band (transient CL)

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quartz of pegmatiteBrattekleiv, Norway

initial

final

initial

after100 s

400 µm

most common CL emission in pegmatitic quartz(hydrothermal quartz)













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Hydrothermal quartz, Freiberg (Germany)

390 nm CL emission band (transient CL)390 nm CL emission band (transient CL)

most common CL emission in hydrothermal quartz(also synthetic quartz !)

initial

after 60s

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finalafter 60s

Initial cathodoluminescence signal and spectralemission after 60 s of electron irradiation













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Agate from Chemitz (Germany)

580 nm CL emission band580 nm CL emission band

400 µm

Hydrothermal quartz, Neves Corvo (Portugal)

most common CL emission in hydrothermal quartz

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secondary

primary

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transient blue CL

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s] yellow CL

Dadoxylon sp.

Primary (yellow CL) and secondary(transient blue CL) silicificationin petrified wood remains fromChemnitz, Germany

quartz sand Camh Rhan quartz sand Haltern

Use of quartz CL colours for evaluatingthe provenance of clastic sediments

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met vol

ign

single source mixed source

ign

Quartz is one of the purest minerals(used as a standard material)

but

it may show very different luminescence behaviour !

2. Crystal chemistry2. Crystal chemistry

LiAl Al

FeTi

Ge

Na

K


Incorporation of activator elements andluminescence behaviour depend on:

1. crystallographic factors

2. specific physico-chemical conditions of crystallisation

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Sm3+Eu2+ Dy3+

Dy3+

Sm3+

Sm3+

Nd3+

Sm3+

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initial

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Mn2+

Svenskenalkaline rock

Ehrenfriedersdorfgranite

Luminescence behaviour of apatite from different geological environments

Feldspar mineralsFeldspar mineralsT site: SiO4/AlO4

tetrahedra

M site: cations(K,Na,Ca,Ba)

Substitution:T site: Fe, Ti, Ga, B, Ge, P, Be, Sn, AlSiPM site: Sr, Ba, Li, Rb, Mn, Cu, Pb, Tl, REE, NH4

MT4O8 alumosilicates

K-Na-Ca series

Ca[Al2Si2O8]anorthite

K[AlSi3O8] sanidineorthoklasemicrocline

Na[AlSi3O8]albite

plagioclase

alka

li fel

dspa

r

Defect centres in feldspar minerals (after Petrov 1994)Defect centres in feldspar minerals (after Petrov 1994)

Thermal stable centres

cations Fe3+ and Mn2+ with d5 electron configuration

Thermal matastable centres(reactivation by natural or artificial irradiation)

cations with uncommon valence (Ti3+, [Pb-Pb]3+)anions with uncommon valence (several types of O- defects)BOm

n radicals (SiO33-, SiO3

3-/Al, PO32-, NO2)

organic radicals (C2H5, CH3)

Most frequent centres responsible for CL in natural feldspars:

O- defects and Mn2+, Fe3+

redox conditions

plagioclase

microcline(amazonite)

Luminescence emissions and associated activators in feldsparsLuminescence emissions and associated activators in feldspars

Activator colour Peak Method Reference

Tl+ UV 280 nm PL Gorobets et al. (1989)

Pb2+ UV 280 nm TL Tarasshchan et al. (1975)

Ce3+ UV 355 nm CL Laud et al. (1971)

Eu2+ blue 420 nm CL,TL,RL Mariano & Ring (1975), Jaek et al. (1996)

Cu2+ blue 420 nm CL,TL,RL Mariano & Ring (1975), Jaek et al. (1996)

Al-O--Al blue 450-480 nm CL,TL,RL Marfunin (1979), Walker (1985)

O--Si...M+ bluish-green 500-510 nm TL,RL Marfunin & Bershov (1970)

Mn2+ yellow 550-570 nm CL,TL Sippel & Spencer (1970)

Fe3+ red/IR 690-740 nm CL,TL,RL Sippel & Spencer (1970), Götze et al. (2000)

REE3+ UV-vis-IR several peaks CL Mariano et al. (1973), Götze et al. (2000)

Pb+ ? IR ~860 nm CL, RL Trautmann et al. (1999), Erfurt (2003)IR

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orthoclaseBodenmais

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Al-O--Al

Si-O-...M2+

Fe3+

OrthoclaseBodenmais (Germany)

CL of feldspar mainly activatedby electron defectsCL of feldspar mainly activatedby electron defects

Albite (Khaldzan Buregte, Mongolia)

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Fe3+ activated CL in feldsparFe3+ activated CL in feldspar

o

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peak

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in n

m

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malkali feldsparterrestrial plagioclaseslunar plagioclases

Shift of the Fe3+ emission in alkali feldspars and plagioclasesin dependence on the chemical composition

Shift of the Fe3+ emission in alkali feldspars and plagioclasesin dependence on the chemical composition

Mn2+ activated CLin feldsparMn2+ activated CLin feldspar

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Mn2+

celsiane, Big Creek

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Mn2+ Fe3+

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o2

anorthite, Monzoni

o1

400 µm

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Fe3+

Changes in Mn2+ and Fe3+

incorporation into feldspardue to varying physico-chemicalconditions of crystallisation

Detection of alteration processes in feldspar(REE3+ activated luminescence)

oo 2

1

300 µm

Pol

albite, Spruce Pine (USA)

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Dy3+

Nd3+

Dy3+ Sm3+

Sm3+

violet CL800

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green CL

Mn2+

18.3 ppm Mn 1.3 ppm Mn

3. Aspects of quantitative luminescence spectroscopy3. Aspects of quantitative luminescence spectroscopy


Factors influencing the luminescence properties/intensityFactors influencing the luminescence properties/intensity

???!!!

sample preparation

analytical conditions(excitation, temperature, etc.)

type of equipment

analytical factors

time(especially transient luminescence)

quenching(e.g. quencher elements - Fe,

concentration quenching)

luminescence activation

sensitizing

crystalllographic factors

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Mn2+

3

2

1

Mn2+ activated CL in calcite

300 µm

oo o3 1 2

Luminescence activation

Correlation of results of quantitative CL with PIXE for the Mn content in carbonates

(Götte & Richter 2004)


Mn2+ activated CL in lunar plagioclases

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o

o

o

o2

4

1

3

2

1

4

3

Luna 24 200 µm

Mn2+

Fe3+Al-O--Al

zone 1 - 7 ppm Mnzone 2 - 31 ppm Mnzone 3 - 23 ppm Mnzone 4 - 14 ppm Mn


SyntheticSynthetic dopeddoped feldsparfeldspar samplessamples ((plagioclaseplagioclase AnAn5050))

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5000 ppm

10000 ppm

Mn2+

Intensity of the Mn2+ activated CL in dependence on the Mn content in feldspar

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8

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4

2

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/ a.

u.

0 20 40 60 80 100 120 140 160Mn content [ppm]

plagioclases

alkali feldspar

rel.

CL

inte

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mol-% Mn0 0.5 1.0 1.5


excitationemission

activatoractivator

excitationradiationlesstransition

luminescence emission concentration quenching

Luminescence quenching

ConclusionsConclusions

ConclusionsConclusionsAs ideal crystal structures practically do not exist, the properties of minerals are determined by their real structure

Luminescence spectroscopy may provide complex information about the defect structure of solids

importance of spatially resolved spectroscopy

There is a close relationship between specific conditionsof mineral formation or alteration, the defect structure and the luminescence properties („typomorphism“)

problem of standardization

For the interpretation of luminescence spectra it is necessary to consider several analytical and crystallographic factors, which influence the luminescence signal

Detection of defects in minerals by luminescence spectroscopy · Luminescence of inorganic and...

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