Basics and Potential of Cathodoluminescence in Metamorphic Petrology

Basics and potential of cathodoluminescence in metamorphic petrology

Jens Götze

Institute of Mineralogy TU Bergakademie Freiberg, Germany ContentContent

1. Basics of luminescence - physical basics - instrumentation - general applications

2. Application of CL in metamorphic petrology - identification of minerals, mineral distribution - primary growth structures - secondary features (deformation - recrystallization - fluid flow - alteration - mineral neoformation) - examples of technical processes

3. Conclusions BasicsBasics ofof luminescenceluminescence LiteratureLiterature Literature

Cathodoluminescence of geological materials

D.J. Marshall

Unwin-Hyman Boston Unwin-Hyman Ltd.

1988 Literature

Springer-Verlag Berlin, Heidelberg, New York 2000

ISBN 3-540-65987-0 Literature

TU Bergakademie Freiberg Akademische Buchhandlung Merbachstraße, PF 203 D-09599 Freiberg

ISBN 3-86012-116-2 Literature

All-Russia Institute of Mineral Resources (VIMS) Moscow 2002

ISBN 5-901837-05-3 HistoryHistory of of cathodoluminescencecathodoluminescence History of Cathodoluminescence

1879 CROOKS Luminescence studies on crystals after bombardment with a cathode ray

1965 SIPPEL, LONG & AGRELL First application for thin section petrography

1965 SMITH & STENSTROM Cathodoluminescence studies with the microprobe

1971 KRINSLEY & HYDE Cathodoluminescence studies with the SEM

1978 ZINKERNAGEL First CL microscope in Germany BasicsBasics ofof luminescenceluminescence

??? Basics of luminescence

LuminescenceLuminescence

= transformation of diverse kinds of energy into 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)

Fluorescence = luminescence emission with a lifetime < 10-8 s

Phosphorescence = luminescence emission with a lifetime > 10-8 s Basics of luminescence

Main processes of luminescence

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

(2) transformation and transfer of the excitation energy

(3) emission of light and relaxation of the system into an unexcited condition Basics of luminescence

UV photoluminescence

Excitation thermal excitation thermoluminescence by energy biological processes bioluminescence

electrons cathodoluminescence

SchematicSchematic model model of of Emission luminescenceluminescence processes processes of light Basics of luminescence Primary electron beam

Back scattered electrons Cathodoluminescence

Secondary electrons

X-rays Auger electrons

Sample

Specimen current Scattered electrons

Unscattered electrons Basics of luminescence

ElectronElectron beam beam interaction interaction with with a a solidsolid

incident electron beam

Sample surface

secondary electrons

back scattered electrons

primary X-ray excitation

2-8 µm continuum radiation cathodoluminescence (Bremsstrahlung) TheThe band band modelmodel Basics of luminescence

E conduction band

conduction band band gap

band gap conduction band

valence band valence band valence band

conductor semiconductor insulator

Energy levels in a band scheme for different crystal types Basics of luminescence

E conduction band

E (photon energy) E

valence band

conductor semiconductor insulator

Electron transitions in a band scheme for different crystal types Basics of luminescence

E Conduction band

donor

acceptor activator

Valence band

(a) semiconductor (b) insulator (small interband spacing) (broad interband spacing)

Positions of ion activator energy levels in a band scheme for different crystal types Basics of luminescence (a) (b) (c) (d) (e)

E 1 2 Conduction band

trap

luminescence

activator

Valence band

Electron transitions and luminescence processes in a solid Basics of luminescence

Conduction band E

radiationless transition

luminescence excitation

activator Valence band

Electron transitions and luminescence in a solid with ion activation TheThe configurational configurational coordinate coordinate modelmodel Basics of luminescence

excited state

absorption ground band state

emission band

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

Stokes shift

Excitation (1) and emission (2) spectra of Mn2+ in calcite (after Medlin 1964) 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) HowHow can can we we use use thethe luminescence luminescence signal signal ?? ?? Basics of luminescence

Visualization of the real structure of solids by CL

Pol CL

Luminescence centres

intrinsic extrinsic

lattice defects trace elements (broken bonds, vacancies) (Mn2+, REE2+/3+, etc.) Basics of luminescence

Types of luminescence centres

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

rare earth elements (REE2+/3+)

2+ actinides (especially uranyl UO2 ) 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

(1) CL microscopy (2) CL spectroscopy

contrasting of different phases determination of the real structure

visualization of defects, zoning detection of trace elements, their and internal structures of solids valence and structural position

2600 apatite Sm3+ 2400 o 2200 2000 3+ 1800 Sm Dy3+ 1600 3+ 1400 Nd Eu2+ 1200 rel. intensity [counts]

1000

800 300 400 500 600 700 800 900 1000 1100 wavelength [nm] CLCL emissionemission spectra spectra Basics of luminescence

TheThe crystal crystal field field theory theory (Burns, 1993)

local environment of the activator ion

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

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

TheThe crystal crystal field field theory theory

local 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. Basics of luminescence

InfluenceInfluence of of thethe crystal crystal field field on on CLCL emissionemission spectra spectra

(1) influence of the crystal field = weak

Dy3+ Dy3+Sm3+Sm3+Dy3+ 16000 3+ Dy zircon

zircon ]

s 12000 t

n scheelite

o c [ 8000 Dy3+

y anhydrite t i 3+

s Sm

n 3+

e Dy

t 3+ calcite

n 4000 Dy 3+ i

Tm 3+

. Sm

l e

r fluorite 0 Tb3+ 300 400 500 600 700 800 apatite wavelength [nm] 400 500 600 700 [nm]

CL spectra of narrow emission CL emission spectra are specific lines (e.g. REE3+) of the activator ion Basics of luminescence

InfluenceInfluence of of thethe crystal crystal field field on on CLCL emissionemission spectra spectra

(2) influence of the crystal field = strong

400 2+ Mn 2+

] calcite Mn activated CL of CaCO3:

n 300

[

t aragonite green (~560 nm)

s 200

n calcite yellow-orange (~610 nm)

e r 100 magnesite red (~655 nm)

300 400 500 600 700 800 wavelength [nm]

CL spectra of broad emission CL emission spectra are specific bands (e.g. Mn2+, Fe3+) of the host crystal Basics of luminescence

500 µm

sea lily stalk (calcite CaCO3)

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

perl (aragonite CaCO3) Basics of luminescence

InfluenceInfluence of of thethe crystal crystal field field onon thethe broad broad CL CL emissionemission bands bands in in solidsolid solutionssolutions

800 plagioclase red IR 750 740 600 730 720

400 710 2+ 3+ Mn Fe 700

200 wavelength [nm] 690 rel. intensity [counts] 680 0 20 40 60 80 100 0 300 400 500 600 700 800 900 An content [mol-%] wavelength [nm]

Position of the Fe3+ activated CL emission band in plagioclases in relation to the anorthite content InstrumentationInstrumentation Scanning Electron Microscope JEOL 6400 with OXFORD Mono-CL detector primary electron beam OXFORD Mono CL

mirror

sample silica-glass fibre guide

Cathodoluminescence detector on a scanning electron microscope Hot-cathode luminescence microscope HC1-LM (designed by Rolf Neuser, Bochum) InstrumentationInstrumentation

hot-cathode microscope cold-cathode microscope

microscope

microscope objective leaded glass thin section viewing point specimen

corona condenser points

optic axis cathode discharge tube focus light source coil h curved electrode hig ge lta vo ble ca CathodoluminescenceCathodoluminescence techniques techniques

SEM-CL CL microscopy polished sample surface polished thin (thick) section focused electron beam, defocused electron beam, scanning mode stationary mode heated filament heated filament („hot cathode“) 20 kV, 0.5-15 nA 14 kV, 0.1-0.5 mA ionized gas („cold cathode“) mirror optics: 200-800 nm (UV - IR) glass optics: 380-1200 nm (Vis - IR) analytical spot ca. 1 µm analytical spot ca. 30 µm panchromatic CL images (grey levels) true luminescence colours resolution << 1 µm resolution 1-2 µm

SE, BSE, EDX/WDX, cooling stage polarizing microscopy, (EDX) CathodoluminescenceCathodoluminescence imaging imaging

SE Polmi

zircon

BSE quartz

10 µm 500 µm

SEM cathodoluminescence Cathodoluminescence microscopy CL microscope with attached CCD based viedeo camera electronic steerage

Computer aided vacuum image analysis pumps

Cathodoluminescence microscope HC1-LM Hot-cathode luminescence microscope HC1-LM

Sample chamber

sample holder

screen

brass clips

sample is fixed Electron gun upside down in the sample holder

transparency ! Wehnelt cylinder CathodoluminescenceCathodoluminescence microscopy microscopy

Polarising microscopy

microscope

sample

filament Light source electron beam Cathodoluminescence microscopy SampleSample preparationpreparation SampleSample preparationpreparation

28 mm

sample holder 1. Polished thin section (glass)

epoxy resin

48 mm sample (~25 µm)

application for all CL equipments SampleSample preparationpreparation

2. Polished section Sample holder (plastics)

epoxy resin

sample piece

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

28 mm

sample holder 4. Sample holder for fluid inclusion (metallic) preparates

sample

48 mm piece

glass plate

application for all CL equipments SampleSample preparationpreparation

3. Polished sample piece

sample piece

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

5. Pressed tablet (powder samples)

pressed tablet of powder sample

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

Coating with conducting material

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

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

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

Convetional photos/slides Digital micrographs Nikon photo camera Digital video camera Kodak Ektachrome 400 HC KAPPA 961-1138 CF 20 DXC

Advantages of CCD:

high spatial resolution

high sentsitivity

- analysis of minerals with very low CL intensities

- low accumulation time

direct combination with image analysis SpectralSpectral CLCL measurementsmeasurements High-resolutionHigh-resolution CLCL spectroscopyspectroscopy

150, 600, 1200 lines/mm 0.4 nm resolution

Silica-glass fibre guide

adaptation (30µm screen)

14 kV, 0.2 mA data processing < 5s accumulation time High-resolutionHigh-resolution CLCL spectroscopyspectroscopy Silica-glass fibre guide

Triple-grating Nitrogen-cooled adaptation spectrograph CCD-detector

CL microscope FactorsFactors influencinginfluencing CLCL properties/intensityproperties/intensity FactorsFactors influencinginfluencing thethe CLCL intensityintensity

sample preparation (sample surface, thickness, etc.)

sample coating (quality, thickness, material, etc.)

temperature

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

time (especially transient CL) AnalyticalAnalytical parametersparameters influencinginfluencing cathodoluminescencecathodoluminescence

1000

2 100 relative intensity relative 10 1 relative intensity relative

0 -120 -100 -80 -60 -40 -20 0 +20 0.1 1 10 100 temperature [°C] Specimen current at 20 kV [nA]

Variation of CL intensity with sample Variation of the intensity of quartz CL temperature for quartz with beam current (modified after Hanusiak & White 1975) (modified after Hanusiak 1975) Sensitizing and quenching

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

Sensitizing of luminescence: typicalQuenching sensitizer of ions:luminescence:

(1) emission-reabsorption (1)(1) ions concentration with intensive quenching absorption („cascade“ luminescence) bands(self in quenching) the UV (e.g. Tl+, Cu+, Pb2+) for sensitization of Mn2+ (2) resonance radiationless (2) quenching by ions with intense (2) ionscharge of transition transfer metals bands (e.g.(e.g. MnFe2+2+,) Cofor2+) (3) nonresonance radiationless sensitization of REE3+ (3) quenching due to lattice defects (3) REE2+/3+ for sensitization of REE3+ (4) thermal quenching emission excitation excitation radiationless transition

activator activator

luminescence emission concentration quenching IntensityIntensity ofof thethe MnMn2+2+ activatedactivated CLCL (ca.(ca. 560560 nm)nm) inin dependencedependence onon thethe MnMn contentcontent in in feldsparfeldspar

10 plagioclases

alkali feldspar 8

4 Intensity / a.u.

2 rel. CL intensity

0 0.5 1.0 1.5 mol-% Mn 0 0 20 40 60 80 100 120 140 160 Mn content [ppm] Concentration quenching („self quenching“) of Mn2+ activated CL in apatite

4.86 wt-% Mn 1.26 o o

o o 3.81 3.41

2.97 o

o 0.85

apatite Vysoki Kamen 300 µm

from Kempe & Götze (2002) MineralMineral groupsgroups andand mineralsminerals showingshowing CLCL in general all insulators and semiconductors elements diamond sulfides sphalerite oxides corundum, cassiterite, periclase halides fluorite, halite sulfates anhydrite, alunite phosphates apatite carbonates calcite, aragonite, dolomite, magnesite silicates feldspar, quartz, zircon, kaolinite technical products (synthetic minerals, ceramics, glasses !) no luminescence of conductors, iron minerals and Fe-rich phases GeneralGeneral applicationsapplications ofof CLCL inin geosciencesgeosciences

identification of minerals, mineral distribution and quantification

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 !)