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