basics of luminescence & cathodeluminance

Basics of luminescenceBasics of luminescence

I

History of cathodoluminescence

History of cathodoluminescence

History of Cathodoluminescence

1879 CROOKSLuminescence studies on crystals after bombardmentwith a cathode ray

1965 SIPPEL, LONG & AGRELLFirst application for thin section petrography

1965 SMITH & STENSTROMCathodoluminescence studies with the microprobe

1971 KRINSLEY & HYDECathodoluminescence studies with the SEM

1978 ZINKERNAGELFirst CL microscope in Germany

2001 International Conference

„Cathodoluminescence in geosciences:New insights from CL in combinationwith other techniques“

Freiberg, Germany

SLMS = Society for Luminescence Microscopy and SpectroscopyKnoxville, USA

Basics of luminescenceBasics of luminescence???

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)

Basics of luminescence

Fluorescence = luminescence emission with alifetime < 10-8 s

Phosphorescence = luminescence emission with alifetime > 10-8 s

Basics of luminescence

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 processesSchematic model of luminescence processes

Excitationby energy

Emissionof light

e-

electrons cathodoluminescence

thermal excitation

biological processes

UV photoluminescence

thermoluminescence

bioluminescence

BioluminescenceBioluminescence

Sample

Back scattered electrons

Secondary electrons

Primary electron beam

Cathodoluminescence

Auger electrons

Scattered electrons

X-rays

Unscattered electrons

Specimen current

incidentelectron beam

continuum radiation(Bremsstrahlung)

cathodoluminescence

Sample surface

back scatteredelectrons

primary X-rayexcitation

secondary electrons

2-8 µm

Electron beam interaction with a solidElectron beam interaction with a solid

incidentelectron beam

sample surface

Electron beam interaction with a solidElectron beam interaction with a solid

Penetration depth of electrons:

R

R = 900 · ρ-0.8 · E01.3 for E0 # 10 keV

R = 450 · ρ-0.9 · E01.7 for E0 > 10 keV

R - penetration depthE0 - electron energyρ - density of the solid

The band modelThe band model

valence band

conduction band

insulatorconductor semiconductor

E

Energy levels in a band scheme for different crystal types

valence bandvalence band

conduction band

conduction bandband gap

band gap

valence band

conduction band

insulatorconductor semiconductor

E

Electron transitions in a band scheme for different crystal types

E (photonenergy)

E

Conduction band

Valence band

E

activator

(b) insulator (broad interband spacing)

(a) semiconductor(small interband spacing)

Positions of ion activator energy levels in a band scheme fordifferent crystal types

acceptor

donor

Valence band

E

activator

luminescence

(e)(a) (b) (c)

trap

(d)

Conduction band21

Conduction band

Valence band

E

activator

luminescence

exci

tatio

n

radiationlessemission

The configurational coordinatemodel

The configurational coordinatemodel

Basics of luminescence

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

Basics of luminescence

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

1

2

Stokes shift

Basics of luminescence

The sensitivity of the electronic states of the Mn2+ ion in octahedral coordination to changes in the intensity of the crystal field splitting Dq and representation in a configurational diagram(modified after Marfunin 1979 and Medlin 1968)

???

How can we usethe luminescence signal ??

How can we usethe luminescence signal ??

Basics of luminescence

Visualization of the real structure of solids by CL

CLPol

Luminescence centres

intrinsic

lattice defects(broken bonds, vacancies)

extrinsic

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

Basics of luminescence

Types of 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.)

Basics of luminescence

Detection of the cathodoluminescence emission

(2) CL spectroscopy(1) CL microscopy

contrasting of different phases

visualization of defects, zoningand internal structures of solids

oapatite

800

1000

1200

1400

1600

1800

2000

2200

2400

2600

300 400 500 600 700 800 900 1000 1100

wavelength [nm]

rel.

inte

nsity

[cou

nts]

Sm3+

Eu2+

Sm3+

Nd3+

Dy3+

determination of the real structure

detection of trace elements, theirvalence and structural position

CL emission spectraCL emission spectra

The crystal field theoryThe crystal field theorylocal environment of the activator ion

- The activator-ligand distances in the different excited states and the slope of the energy levels depend on theintensity of the crystal field(expressed as crystal field splitting = 10Dq)

- The stronger the interaction of the activator ion with thelattice, the greater are the Stokes shift and the width of the emission line.

(Burns, 1993)

The crystal field theoryThe crystal field theorylocal environment of the activator ion

Factors influencing values of or 10Dq are:

- type of the activator ion (size, charge)

- type of the ligands

- the interaction distance

- local symmetry of the ligand environment

etc.

300 400 500 600 700 800

wavelength [nm]

0

16000

12000

8000

4000

rel.

inte

nsity

[cou

nts]

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 CL emission spectraInfluence of the crystal field on CL 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+)

ENERGY LEVELS OF THE REE3+

Basics of luminescence

Energy levels diagram and emission spectrum of Eu3+ in Eu2(SO4)3 * 8H2O (after Marfunin 1979)f - oscillatory strength (effectiveness of excitation); A - probability of emission transitions

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

(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

300 400 500 600 700 800wavelength [nm]

100

400

300

200

rel .

inte

n si ty

[co u

n ts]

Mn2+ activated CL of CaCO3:

aragonite green (~560 nm)

calcite yellow-orange (~610 nm)

magnesite red (~655 nm)

perl (aragonite CaCO3)

sea lily stalk (calcite CaCO3)500 µm

Visual and spectral detection of Mn2+ activated CL in natural carbonates

Mn2+-distribution in crystal hetero-structures:CaCO3 and MgCO3-cluster in Mg-Calcite

Habermann (2001)

Cation positions ofcommon luminescencecentres in silicates

(Ramseyer & Mullis 2000)

Influence of the crystal fieldon the broad CL emission bands in mixed crystals

Influence of the crystal fieldon the broad CL emission bands in mixed crystals

plagioclase

Fe3+Mn2+

0

800

600

400

200rel.

inte

nsity

[cou

nts]

300 400 500 600 700 800 900wavelength [nm]

750

740

730

720

710

700

690

680

wav

elen

gth

[nm

]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

InstrumentationInstrumentation

Scanning Electron Microscope JEOL 6400with OXFORD Mono-CL detector

samplesilica-glassfibre guide

primary electron beam

mirror

Cathodoluminescence detector on a scanning electron microscope

OXFORD Mono CL

Hot-cathode luminescence microscope HC1-LM(designed by Rolf Neuser, Bochum)

Cold-cathode luminescence microscope (CITL)(Cambridge Instruments)

Cold-cathode luminescence microscope with EDX detector(Cambridge Instruments)

(Vortisch et al. 2003)

cold-cathode microscopehot-cathode microscope

InstrumentationInstrumentation

leaded glassviewing point

microscope

thin section

coronapoints

condenser

light sourcedischarge tube

curved electrodehigh

voltage

cable

optic axis

specimen

microscopeobjective

focuscoil

cathode

Cathodoluminescence techniquesCathodoluminescence techniques

CL microscopySEM-CL

polished thin (thick) section

defocused electron beam, stationary mode

heated filament („hot cathode“)14 kV, 0.1-0.5 mA

ionized gas („cold cathode“)

glass optics: 380-1200 nm (Vis - IR)

analytical spot ca. 30 µm

true luminescence colours

resolution 1-2 µm

polarizing microscopy, (EDX)

polished sample surface

focused electron beam,scanning mode

heated filament 20 kV, 0.5-15 nA

mirror optics: 200-800 nm (UV - IR)

analytical spot ca. 1 µm

panchromatic CL images (grey levels)

resolution << 1 µm

SE, BSE, EDX/WDX, cooling stage

Cathodoluminescence imagingCathodoluminescence imaging

zircon

CL

SE

BSE

10 µm

CL

Polmi

500 µm

quartz

Cathodoluminescence microscopySEM cathodoluminescence

Cathodoluminescence microscope HC1-LM

Computer aidedimage analysis

vacuumpumps

electronicsteerage

CL microscope withattached CCD basedviedeo camera

brassclips

screen

sampleholder

Sample chamber

Wehnelt cylinder

Electron gun

Hot-cathode luminescence microscope HC1-LM

sample is fixedupside down inthe sample holder

transparency !

microscope

sample

Light sourcefilamentelectron

beam

Polarisingmicroscopy

Cathodoluminescencemicroscopy

Cathodoluminescence microscopyCathodoluminescence microscopy

Sample preparationSample preparation

Sample preparationSample preparation

1. Polished thin section sample holder(glass)

epoxy resin

sample(~25 µm)

48 m

m

28 mm

application for all CL equipments

Sample preparationSample preparation

2. Polished section Sample holder(plastics)

application for SEM-CL („cold-cathode“ microscopes)

epoxy resin

samplepiece

Sample preparationSample preparation

4. Sample holder for fluid inclusionpreparates

sample holder(metallic)

glassplate

48 m

m

28 mm

application for all CL equipments

samplepiece

Sample preparationSample preparation

3. Polished sample piece

samplepiece

application for SEM-CL („cold-cathode“ microscopes)

Sample preparationSample preparation

5. Pressed tablet (powder samples)

application for SEM-CL („cold-cathode“ microscopes)

pressed tabletof powder sample

Sample preparationSample preparation

for SEM-CL and „hot-cathode“ CL microscopes

Coating with conducting material

- to prevent the built up of electrical charge during electron irradiation

- coating material: C, Au, Al, Ag, Cu

DocumentationDocumentation

DocumentationDocumentation

Digital video cameraKAPPA 961-1138 CF 20 DXC

Digital micrographsConvetional photos/slides

Nikon photo cameraKodak Ektachrome 400 HC

Advantages of CCD:

high spatial resolution

high sentsitivity

- analysis of minerals withvery low CL intensities

- low accumulation time

direct combination withimage analysis

Spectral CL measurementsSpectral CL measurements

High-resolution CL spectroscopyHigh-resolution CL spectroscopy

14 kV, 0.2 mA< 5s accumulation time

adaptation(30µm screen)

Silica-glassfibre guide

150, 600, 1200 lines/mm 0.4 nm resolution

data processing

adaptation

High-resolution CL spectroscopyHigh-resolution CL spectroscopy

Triple-gratingspectrograph

Nitrogen-cooledCCD-detector

Silica-glass fibre guide

CL microscope

Factors influencingCL properties/intensityFactors influencingCL properties/intensity

Factors influencing the CL intensityFactors influencing the CL intensity

time(especially transient CL)

sample preparation(sample surface, thickness)

sample coating(quality, thickness, material)

temperature

analytical conditions(acceleration voltage, beam current, vacuum, etc.)

type of equipment

analytical factors crystalllographic factors

quenching

luminescence activation

sensitizing

Basics of luminescence

Analytical parameters influencing cathodoluminescenceAnalytical parameters influencing cathodoluminescence

-120 -100 -80 -60 -40 -20 0 +20

Specimen current at 20 kV [nA]

rela

tive

inte

nsity2

0

1000

3

Variation of the intensity of quartz CLwith beam current(modified after Hanusiak 1975)

rela

tive

inte

nsity

1

100

10

100

temperature [°C]

1

0.1 1 10

Variation of CL intensity with sampletemperature for quartz(modified after Hanusiak & White 1975)

Basics of luminescence

Sensitizing and quenching

Interaction between two or more ions with transfer of ecitation energyfrom one ion to another resulting in changes of their luminescence.

Quenching of luminescence:

(1) concentration quenching(self quenching)

(2) quenching by ions with intensecharge transfer bands (e.g. Fe2+, Co2+)

(3) quenching due to lattice defects

(4) thermal quenching

Sensitizing of luminescence:

(1) emission-reabsorption(„cascade“ luminescence)

(2) resonance radiationless

(3) nonresonance radiationless

typical sensitizer ions:

(1) ions with intensive absorptionbands in the UV (e.g. Tl+, Cu+, Pb2+)for sensitization of Mn2+

(2) ions of transition metals (e.g. Mn2+) forsensitization of REE3+

(3) REE2+/3+ for sensitization of REE3+

excitationemission

activatoractivator

excitationradiationlesstransition

luminescence emission concentration quenching

Influence of excitation energy and delay time on emission spectra oflaser-induced time-resolvedluminescence(apatite Ehrenfriedersdorf, Germany)

(Kempe & Götze 2002)

Basics of luminescence

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 !)

no luminescence of conductors, iron minerals andFe-rich phases

CL of orthopyroxene (with carbonate) from an alkaline complex, Namibia

300 µm

General applications of CL in geosciencesGeneral applications of CL in geosciences

identification of minerals, mineral distribution andquantification

typomorphic properties(CL colour, CL behaviour, spectral characteristics)

crystal chemistry(trace elements, internal structures, zoning)

reconstruction of geological processes

characterisation of technical products(also non-crystalline phases !)

calcite

feldspar

quartz?

Identification of minerals

Mineral distribution

Quantification of mineral abundance

Identification of minerals

Mineral distribution

Quantification of mineral abundance

Identification of minerals - mineral distribution - textureIdentification of minerals - mineral distribution - texture

500 µm

Q

Kf

Plag

CLPol

Applications of CL

Identification of minerals - mineral distributionIdentification of minerals - mineral distribution

400 µm

QF

C

zircon

kaolinite

500 µm

500 µm

Pol CL

Quantification of mineral abundance by combined CL and image analysisQuantification of mineral abundance by combined CL and image analysis

Aim:

- quantification of phases in addition to conventional methods

Limits of other methods:

- chemical analysis provides no information concerning phase composition- X-ray diffraction without information concerning texture, intergrowth, etc.

limited application for non-crystalline samples - polarizing microscopy is time consuming, limits for fine-grained samples

Advantages of combined CL and image analysis:

- clear phase contrast by CL and automatization of analysis bycomputer aided image analysis

- comparison of optical and CL microscopy possible- information concerning texture, phase distribution, grain size, porosity, etc.- only one thin section necessary

Cathodoluminescence microscope HC1-LM

Computer aidedimage analysis

vacuumpumps

electronicsteerage

CL microscope withattached CCD basedviedeo camera

Image processing algorithm:

(1) shadow correction by means of low-pass filtering(2) basic image processing (focus, contrast, brightness, etc.)(3) definition of the CL colours of the different mineral phases by

combining the values of colour and brightness(4) false-colour imaging of the different phases (thresholding) and

conversion to binary mode(5) processing of phases in the binary mode(6) definition of options and measuring(7) extraction of data and interpretation

the number of fields of view depends on:

- the homogeneity/heterogeneity of the sample- magnification- contents of mineral phases analysed

Quantitative CL microscopy of synthetic standard samplesQuantitative CL microscopy of synthetic standard samples

CLPol

300 µm

Q

QC

Q

C

F

C

F

F

60

50

40

30

20

10

%

alkali feldspar magnetitequartz

1 0.54 0.72

45 45.7 46.345 45.7 46.3

5 5.3 4.5

calcite

calibrated composition

weight-%

vol-%

analysed composition

vol-%

Quantification of mineral abundance by combined CL and image analysisQuantification of mineral abundance by combined CL and image analysis

Binary mode

CL image

Thresholding

Quantification offeldspar content

quartzfeldsparcarbonatekaolinitepore space

Mineral composition ofCretaceous sandstonesof the Elbe valley, Germany(Magnus & Götze 1997)

Typomorphic properties of mineralsTypomorphic properties of minerals

First classification of quartz types according to their CL propertiesafter ZINKERNAGEL (1978)

Typomorphic CL properties of quartzTypomorphic CL properties of quartz

schist

rhyolitegranite

hydrothermal

Applications of CL

Li

Al Al

FeTi

Ge

Na

K

Crystal chemistryCrystal chemistry

- trace-elementdistribution

- quantification ??

fluoriteChemnitz, Germany

100 µm

oo21

1600

1200

800

400

0

rel.

Inte

nsity

[cou

nts]

300 400 500 600 700 800wavelength [nm]

1

2

Er3+Eu2+

Dy3+

Dy3+

Sm3+

Dy3+ Sm3+

Dy3+

fluorite, Chemnitz (Germany)

Applications of CL

Crystal chemistryCrystal chemistry

18O

16O

Isotope geochemistryIsotope geochemistry

Application of CL in isotope geochemistry and geochronology

Application of CL in isotope geochemistry and geochronology

detection of internal structures,zoning and alteration featuresin samples for the analysis ofstable isotopes

detection of relic cores andinternal structures in zirconused for age dating

General applications of CL in geosciencesGeneral applications of CL in geosciences

identification of minerals, mineral distribution andquantification

typomorphic properties(CL colour, CL behaviour, spectral characteristics)

crystal chemistry(trace elements, internal structures, zoning)

reconstruction of geological processes

characterisation of technical products(also non-crystalline phases !)

Characterisation of technical productsCharacterisation of technical products

Technical and industrial applications:

- ceramics

- refractory materials

- glass

- waste materials

- building stones and materials

- archeometry

- biomaterials etc.

Al content and cathodoluminescence in silica glass

Applications of CL

Glass Glass