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Raman and Raman and

fluorescence fluorescence

Gérard PANCZER,

LPCML, UCBL, Villeurbanne, France

gerard.panczer@univ-lyon1.fr

Michael GAFT,

LDS, Petach Tikva, Israel

Georaman international school

“Applications of Raman spectroscopy to Earth

Sciences and Cultural Heritage

14 to 16 th of June 2012, Nancy (France)

Fiat Lux ! Fiat Lux ! (Fluorescence vs Raman) (Fluorescence vs Raman)

Electronicground state

1st ElectronicExcited State

Exc

itatio

n E

nerg

y, σ

(cm

–1)

Vibrationalstates

4,000

25,000

0 IRσ

σ σemit.

2nd ElectronicExcited State

Raman∆σ=σemit.–σ

σ ±∆σ

Stokes

Anti-StokesIntermediate virtual states

Rad

iativ

e el

ectr

onic

tran

sitio

ns

Flu

ores

cenc

e

Abs

orpt

ion

MNHN Grand Sapphire Louis XIV (MNHN)

Mobile mini Raman, 532 nm

Outlines

• Fluorescence vs Raman

• How to get rid of fluorescence (and of thermal

emission) ?

– luminescent centers

– HT Raman

• How to take advantage of fluorescence

(photoluminescence, light emission) ?

• How to play with time ?

– Gated Raman,

– TR PL

• Some various examples

fluorescence

Schematic representation of luminescence

A

BC

D

M0

M

Energie

Etat fondamental

Etat excité

hνννν

A-B : absorption(excitation)

B-C : thermalization 1

hνννν’ < hνννν

C-D : emission(desexcitation)

D-A : thermalization 2

Fluorescence vs Raman

FluorescenceElastic diffusion

(Rayleigh)

Inelastic diffusion (Raman)

Probability (~) 10-4 à 10-2 10-2 à 10-1 10-7 à 10-14

Advice 1: Use safety

goggles (filters)

� For security

� To see the potential

fluorescence

Luminescent centers 1: Intrinsic emissionsLuminescent centers 1: Intrinsic emissions

4 5 6 7

(TiO4)4- (VO

4)3- (CrO

4)2- (MnO

4)-

(ZrO4)4- (NbO

4)3- (MoO

4)2-

(TaO4)3- (WO

4)2-

Opticaly active groups

responsible for intrinsic emissions

and (UO2)2+

Intrinsic emissionsIntrinsic emissions

360 nm

(MoO4)2- in powellite, CaMoO4

360 nm

(WO4)2- in scheellite, CaWO4

Luminescent centers: ions (<%)

4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

Transitions ions 3dn d10 Heavy ions 4-6s2 4-

6s p

Ti3+ V2+

Cr2+

Cr3+

Cr4+

Cr5+

Mn2+

Mn4+

Mn5+

Fe3+ Co2+ Ni2+ Cu+ As3+

Ag+ In+ Sn2 Sb3+

Tl+ Pb2+ Bi3+

Lanthanides 4fn-4fn-1 5d

La Ce3+ Pr3+ Nd3+ Pm3+ Sm3+

Sm2+

Eu3+

Eu2+ Gd3+ Tb3+ Dy3+

Dy2+

Ho3+

Ho2+

Er3+

Er2+

Tm3+

Tm2+ Yb3+ Lu

Actinides 5fn

Ac Th4+ Pa4+ U6+ Np3+ Pu3+ Am3+ Cm3+ Bk3+ Cf3+ Es3+ Fm3+ Md3+ No3+ Lr

Luminescent ions responsible for

extrinsic emissions

Extrinsic emissionsExtrinsic emissions

Eu3+ and Pr3+ doped powellite Cr3+ doped corundum

Rare earth ions luminescence characteristics

Transitions / shape Decay Time

Rare earth ions 4f – 4f long

Nd3+, Sm3+, Sm3+, Eu3+,

Gd3+, Tb3+, Dy3+, Yb3+Lines ~10 µs - 1 ms

Rare earth ions 5d – 4f short

Ce3+ Bandfully allowed

(~ 10 - 100 ns)

Eu2+ Band ~ 1 µs

Yb2+, Sm2+ Band 100 µs - 1 ms

What is the decay time of Raman scattering ?

≈ duration of the excitation:

•For CW laser, Raman scattering is not dependant

• For nanosec range pulsed laser, Raman scattering is ≈

10 ns (duration of the laser pulse)

Transition metal luminescence characteristics

Transitions / shape Decay Time

Transition metal ions d - d long

Cr3+ 2E - 4A2 line(s) 1 ms

Cr3+ 4T2 - 4A2 band ~ 10 - 100 µs

Mn2+, Fe3+ 4T1 - 6A1 ; 4T2 - 6A1 band ~ 1 ms

1 2 3 4 GPa

Cr3+ doped corundum (ruby)

widely use as pressure gauge

in DAC

550 600 650 700 750 800 8500

10000

20000

30000

Molecular group luminescence characteristics

Transitions / shape Decay Time

d0 complex ions Charge-transfer

(VO4)3-, (WO4)2-,

(MoO4)2- , (TiO4)4-Band

relatively short

(10 - 100 µs)

(UO2)2+ Band Long (~100 µs - 1 ms)

Glass UO22+ !!

0 500 1000 1500 20000

200000

400000

600000

800000

1000000

1200000

Décroissance des luminescences : Eu3+ (τ

1/2= 300 µs)

MoO4

2- (τ1/2

= 15 µs)

Inte

nsité

Temps (µs)

532 nm exc.

Microluminescence (355 nm)

20 µm

20 µm

500 6000,0

5,0x104

1,0x105

1,5x105

602

573

547

524

502

nm

I (A

.U.)

Uranyl (UO2)2+

in autunite Ca(UO2)2(PO4)2.10H2O

Advice 2: Pay attention:

� Luminescence detection limit

can be in certain case below ppm !

�So be ready to have numerous

luminescent centers even in

synthetic samples (purity 99,99 %

...)

� don’t be frightened; try to

identify them.

Advice 2: Pay attention:

� Luminescence detection limit

can be in certain case below ppm !

�So be ready to have numerous

luminescent centers even in

synthetic samples (purity 99,99 %

...)

� don’t be frightened; try to

identify them.

Gaft, M. et al. (2005) Luminescence Spectroscopy of Minerals and Materials. Springer Verlag, Berlin.

How to get rid of fluorescence ?

Advice 3: Read the Raman

equipment instructions !

�To record (of course) spectra in

relative wavenumber unit (cm-1)

�To record and to explore the

whole spectral range up to 1000 nm

� to identify the nature of the

luminescence.

� to choose the optimum excitation

to avoid luminescence

Advice 3: Read the Raman

equipment instructions !

�To record (of course) spectra in

relative wavenumber unit (cm-1)

�To record and to explore the

whole spectral range up to 1000 nm

� to identify the nature of the

luminescence.

� to choose the optimum excitation

to avoid luminescence

Excitation ≈

absorptionemission

λ (nm)

Black body and thermal emission

T

3

max

10897.2 −×=λ

λmax wavelength (in m)

T (in Kelvin)

Djeva (Montey)

( )1

12,

5

2

−×=

kThce

hcTE λλ

λ

E(l,T) energy intensity emitted at wavelength λ(m)

T (Kelvin)

H Planck constant = 6.625 x 10-34 J.sec;

k Boltzmann cst =1.38 x 10-23 J/K

c speed of light = 3 x 108 m/sec

1000 nm100 nm

HT Raman: get down ! (in wavelength)

UV visible NIR/IR

244 nm (Argon) 458 nm (Ar, blue) 785 nm (diode)

257 nm (diode) 473 nm (diode, blue) 830 nm (diode)

325 nm (He-Cd) 488 nm (Ar, blue)

363.8 nm (Ar) 514 nm (Ar, green) 1064 nm (YAG, IR)

532 nm (YAG, green)

633 nm (HeNe, red)

647 nm (diode, red)

Reynard et al., EMU Notes in Mineralogy, 12 (2012), Chapt. 10, 365–388

HT Raman

200 400 600 800 1000 1200 1400 1600 18000

1x104

2x104

3x104

4x104

325 nm

473 nm633 nm

I

Wavenumber (cm-1)

Heating stages (heating Pt wire and

1500 Linkam)

Lanthanum boro-germanate glass at 1173 K (900 °C) in

which crystallized LaBSiO5 stillwellite for different

excitations (de Ligny, LPCML)

Daniel, I. et al., (1995) Phys Chem Minerals, 22, 74-86.

Neuville D. R. et al., (2007) X-Ray Absorption Fine Structure - XAFS13, 882, 413-415

Raman shift = relative wavenumber (cm-1)

100 200 300 400 500 600 700 800 900 1000

780 nm

532 nm

633 nm

325 nm

Eu3+

Eu3+

Eu3+

Nd3+

Nor

mal

ized

Inte

nsity

Raman Shift (cm-1)

Eu, Nd, Na:Powellite

Nd3+

x

x

νλ

λ−

∗

=−7

0

7

10

110

• wavelength λx

(nm)

• excitation λ0

(nm)

• relative

wavenumber (cm-1)

xν

328 330 332 334

0,0

0,5

1,0

782 nm633 nm

532 nmN

orm

aliz

ed In

tens

ity

Wavelength (nm)

325 nm

535 540 545 550 555 560

0,0

0,5

1,0

Eu3+

Nd3+

Nd3+

Eu3+

Nor

mal

ized

Inte

nsity

Wavelength (nm)

Eu3+

635 640 645 650 655 660 665 670

0,0

0,5

1,0

Nor

mal

ized

Inte

nsity

Wavelength (nm)

790 800 810 820 830 840

0,0

0,5

1,0

Nor

mal

ized

Inte

nsity

Wavelength (nm)

Wavelength (nm) or absolute wavenumber (cm-1)

13

mm

ν1(Ag)

ν3(Eg, Bg)

ν4(Bg)

ν2(Ag+Bg)R

T

Conversion

• From relative vawenumbers to wavelength:

• The intensity of the Raman signal is inversely proportional to the

fourth power of the laser wavelength λ0:

I1/I2 = (λ2/ λ1)4

I248 = 21× I532 = 100×I785

x

x

νλ

λ−

∗

=−7

0

7

10

110

• wavelength λx (nm)

• excitation λ0 (nm)

• relative wavenumber (cm-1)

4)1

( −≈λRI

Polarized Raman and fluorescence

200 400 600 800 1000 1200 1400

Z(XR)Z

X(YR)X

X(ZR)X

Raman shift (cm-1)

I

Z(XR)Z

X(YR)X

X(ZR)X

964

581

550 600 650 700 750 800 850 900Wavelength (nm)

I

579

870

Ramanrange

E

Z

X

E

X’

X

E

X

Z

Mn2+

Nd3+

ν1 streching (PO4)

ν4

bending

ν2 bending

ν3

streching

Fiesch apatite (Alpes)

Porto notation

Ex: Tetragonal (a = b ≠ c ; α = β = γ =

90°

Z(XR)ZX(ZR)XX(YR)X =

X(X’R)X

E

E

E

Porto, S.P.S. & Scott, J.F. (1967) Physical Review, 157, 716-719.

Advice 4: Turn you sample !

(if anisotropic)

The luminescence can be as

well polarized.

Advice 4: Turn you sample !

(if anisotropic)

The luminescence can be as

well polarized.

Gated Raman

M. Gaft & L. Nagli, Opt. Mat. 30 (2008) 1739–1746

UV gated Raman spectroscopy

for standoff detection of

explosives (organic matters)

Needed:

• pulsed laser

• delay and temporal gate

generator

• time resolved detection

(ICCD)…

Time-resolved photoluminescence

Delay generator

Sample

Cryostat

Spectrometer(gratting400 or 1200 l/mm

Opticalfiber

Dye

(>= 4 ns)

ICCD

ext. trig.

fire

To

trig

LASER

cd

GPIB

EximerYAG

Cooler

ICCD

delay

generator

microscope

Pulsed

laser

Time resolved photoluminescence equipment

100 200 300 400 5000

3

6

9

12

temps, µµµµs450 500 550 600 650 700 750

0,0

5,0x104

1,0x105

1,5x105

2,0x105

2,5x105

Eu3+

Sm3+

Eu3+

Sm3+Dy3+

Dy3+

rela

tive

inte

nsity

(A

.U.)

wavelength (nm)

Delay 200 µs Gate 1 ms

Delay 1 µs Gate 1 ms

450 500 550 600 650 700 750

5,0x104

1,0x105

1,5x105

2,0x105

Dy3+

Dy3+

Eu2+

rela

tive

inte

nsity

(A

.U.)

wavelength (nm)

450 500 550 600 650 700 750

5,0x104

1,0x105

1,5x105

2,0x105

2,5x105

Eu2+

Ce3+

rela

tive

inte

nsity

(A

.U.)

wavelength (nm)

Delay 0 Gate 1 ms

Laser pulse

450 500 550 600 650 700 750

5,0x104

1,0x105

1,5x105

2,0x105

2,5x105

Dy3+

Dy3+

rela

tive

inte

nsity

(A

.U.)

wavelength (nm)

Delay 50 µs Gate 1 ms

Gated spectroscopies and time-resolved luminescence

τ = 4 µs

τ = 40 µs

τ = 900 µs

τ/0

tt eII −=

Gated Raman

1000 1500 2000 25000,0

5,0x105

1,0x106

1,5x106

2,0x106

2,5x106

3,0x106 λλλλex

=532 nm cw

I

cm-1500 1000 1500 2000 2500

0,0

5,0x105

1,0x106

1089

Mn2+

ττττ=11 ms

I

Raman shift (cm-1)

500 1000 1500 2000 2500

6,0x104

8,0x104

1,0x105

G=10 ns

I

Raman shift (cm-1)

λex=532 nm pulsed

Delay=0

Gate=10 ns

λex=532 nm pulsed

Delay=0

Gate=15 ms

λex=532 nm

CW continueous

Advice 5:

To conduct good gated

Raman,

shut it as much as you can !

(the gate).

Advice 5:

To conduct good gated

Raman,

shut it as much as you can !

(the gate).

Gaft M. & Nagli L., Eur. J. Mineral. 2009, 21, 33–

42

UV gated Raman (266 nm)

1000 2000 3000 4000

5

10

1000 2000 3000 4000

5

10

1000 2000 3000 4000

500

1000

1500

1000 2000 3000 40000

200

400

1000 2000 3000 40000

500

1000

1500

1000 2000 3000 40000

100

200

300

3426.4869 3152.303357

0.25

796

827.

7907

1038

.795

9

2244

.405

5

3028

.735

1

3544

.419

680.

345

975.

476

1085

.43

1189

.59

3770

.54

917.

607

1160

.66

3944

.15

625.

4613

6

1009

.954

311

33.1

28

1626

.401

3410

.646

3488

.450

7

Inte

nsity

(a.

u.)

Inte

nsity

(a.

u.)

Inte

nsity

(a.

u.)

Water

Ice

Apophyllite

Raman Shift, cm -1

KCa4Si

8O

20(F,OH)x8H

2O

PyromorphitePb

5(PO

4)3Cl

TopazAl

2SiO

4(F,OH)

2

Gypsum

Raman Shift, cm -1

CaSO4x2H

2O

M. Gaft, L. Nagli. European Mineral. J, 2009, 21, 33–42.

λex=266 nm

Raman cross-section of

H2O at 248 nm is

• 120 times larger than

at 532 nm and

• 120 times larger than

at 785 nm

because of pre-

resonance

enhancement.

Why and how to get advantage from fluorescence?

• Raman probes medium to short range order,

while

• Fluorescence probes short range order

(sensitivity to local environment around the

luminescent ion)

• Luminescents trace elements (REE) are often

tracers of genetic conditions

Materials FOR optics

Optical materials Synthetic Natural analogues

Phosphors (Ce3+, Tb3+) : LaPO4Pr3+: CaWO4(Cu+, Al3+): ZnS; Mn2+: ZnSCe3+:Y5(SiO4)3FTb3+: LaSiO 2F(Ce3+, Tb3+):Gd4(Si2O7)F2Tb3+ : CaYSi3O3F4

MonaziteScheeliteSphaleriteBritholite

WollastoniteCuspidine

Melilite

Scintillators Ce3+ : CaWO4Ce3+ : PbWO4Ce3+ : YbPO4Pr3+ : CaTiO3

ScheeliteStolzite

XenotimePerovskite

Dosimeters U6+ : CaF2 ; REE3+ : CaF2(Dy3+, Tb3+) : CaSO4(Cr3+, Ti3+) : Al 2O3

FluoriteAnhydriteCorundum

Laser Materials REE3+: CaWO4REE3+: CaMoO4(Cr3+, Cr4+): Y3Al 5O12(Cr3+, Ti3+): BeAl 2O4REE3+: ZrSiO 4Cr4+: Mg2SiO4Mn5+: Sr5(PO4)3(Cl, F)Yb3+: Sr5(PO4)3(Cl, F)Mn2+: (Ca, Sr, Ba)2(PO4, VO4)ClCr3+: (Ca, Sr)(Y, Gd) 4Si3O13(Nd3+, Ho3+): Ca5(PO4)3F

ScheeliteMolybdenite

GarnetAlexandrite

ZirconForsterite (olivine)

F, Cl ApatiteApatite

Spodiosite (Apatite)Apatite

Fluorapatite

phosphors

400 500 600 7000

1x105

2x105

nm

I

Luminophores RVB (exc. 365 nm)

5 µm

100 µm

Spectre d’émission globale

5 µm

400 500 600 7000

1x106

2x106 Eu2+

nm

I

BAM (BaAl 10MgO17:Eu2+)

400 500 600 7000,0

5,0x105

1,0x106

1,5x106

Mn2+

nm

I

Zn2SiO4:Mn 2+

400 500 600 7000,0

5,0x105

1,0x106 Eu3+

nm

I

Y2O3:Eu3+

Microphotoluminescence of RGB phosphors

Panczer G. etal. (2003) J. Optical Material, 24, 1-2, 253-257

Raman and fluorescence: some examples

• Self irradiation in minerals

– U bearing powellite CaMoO4

– monazites (La,Ce)PO4

• Cultural heritage (on site analyses)

– Chauvet cave (30 000 yrs)

– Grand sapphire of Louis XIV

Raman and fluorescence of Mo rich glass ceramic

νννν1

νννν2

νννν4 νννν3

Mo-O

575 600 625 800 825

0

15000

30000

45000

Glassy matrix

Crystalline phase

Eu3+

Nd3+

4F5/2

+2Η9/2

→4I9/2

5D0→7F

2

5D0→7F

1

Inte

nsity

Wavelengh (nm)

5D0→7F

0

Ceramic

Raman fluorescence

BSE

Ex.1: U bearing powellite CaMoO4 (Kazakhstan)

PL Pr3+

9,0 cm-1

12,1 cm-1

20 µm

BSE878 cm-1 Raman

FWHM

0 50 100 150 200 250

9

10

11

12

FW

HM

(cm

-1)

Distance (µm)

Mapping desorder (chemical and radiation induced)

Luminescence mapping of incorporated REE (exc. 532 nm)

600 700 800 900

[UO2]2+

Er3+

Nd3+

Nd3+

Inte

nsité

Longueur d'onde (nm)

Pr3+

Pr3+ Er3+ Nd3+Type

[UO2]2+

)

� Uranium and REE are concentrated during the crystal growth history as

in the synthetic glass ceramic

Mendoza, C. et al., (2012) Am. Min. (submitted)

Ex.2: Self irradiations in monazites (La,Ce)PO4

Trimouns YS35 Moacir DIG19 Manangotry

Locality France China Brazil Canada Madagascar

ThO2

(wt %)nd

5.74–

15.606.92 9.03–10.33 13.25

UO2

(wt %)nd

0.29–

0.940.13 0.14–0.46 0.20

Age

(My)99 24 474 1928 545

Ref.

Schärer

et al.

(1999)

Schärer

et al.

(1994)

Seydoux-

Guillaume et al.

(2002b)

Schärer &

Deutsch

(1990)

Paquette et

al. (1994)

Natural monazites from various localities, age and Th and U content

Raman and disorder in monazites (La,Ce)PO4

Ruschel K. et al. (2012) Miner Petrol , 105, 41–55

Substitution induced disorder Annealing of radiation induced disorder

Nd3+ luminescence and disorder in natural monazites

800 825 850 875 900 925

0,0

0,5

1,0

4F3/2

→4I9/2

4F5/2

+2H9/2

→ 4I9/2

TRIM

DIG

MADA

MOAC

Nor

mal

ized

I (A

U)

Wavelength (nm)

YS

Manangotry

(Madagascar),

DIG19 (Canada),

Moacir (Brazil),

YS35 (China),

Trimouns (France)

Note the broadening of the 4F3/2 �4I9/2 Stark

sublevels.

Panczer G. et al. (2012) EMU Notes Book in Mineralogy Series, (J. Dubessy & F. Rull, editors). 12, 1–22.

514 nm

y = 0,0637x + 2,8383

R2 = 0,9474

1,0

2,0

3,0

4,0

5,0

6,0

7,0

8,0

9,0

0 5 10 15 20 25 30

ThO2 (wt%)

FW

HM

line

1 ~

863

nm

Gd

Ce

Nd

La,Nd

McG

osr

eE

mb

ala

an

Moa

cir

Are

nd

al

Dig

19Y

S3

5

Mad

agas

car

500°C

700°C

800°C900°C

1000°C500°C

700°C800°C900°C

1000°C

500°C

700°C

800°C

900°C

1000°C

FWHM Nd3+ 573 nm line vs annealing

ThO2 (wt %)

Maximum natural

irradiation level

Synthetic monazites

Natural monazites

annealing

Zero irradiation level

Ex.3: On site analyses Chauvet cave (Ardèche, France)

Upper Paleolitic

30 000 years old

Phosphates (bones, tooth,

phosphatic concretions)

Fluorescence

in Chauvet cave

450 500 550 600 650 7000

50

100

150

200

250

300

350

400

Inm

Raman and fluorescence on Chauvet site

400 600 800 1000 1200 1400 1600 18000

500

1000

1500

2000

2500

3000

713,78

1088,36

283

raman stalactite calcite 1 532 nm(début solarisation)

I

cm-1

500 1000 1500 20000

500

1000

950 Raman 785 nmvertebre 2

I

cm-1

calcite

apatite

Raman

Luminescence

490 nm Irradiation induced

defect (Rn*) in calcite

or

fulvique acid

fluorescence ???

Gaft M. et al. Am. Min., 93 (2008) 158–167

Perrette Y. et al. Chemical Geology 214 (2005) 193– 208

Ex.4: On site analyses of the Grand sapphire (Louis XIV)

600 700 800 900 1000

0

500

1000

1500

2000

2500

3000

3500

4000 Grand saphir luminescence 532 nm

Inte

nsity

(A

U)

wavelength (nm)

500 1000 1500

5,0x102

1,0x103

Inte

nsity

(A

U)

Raman shift (cm-1)

Grand sapphire 785 nm 532 nm

Luminescence Cr3+

in SCF

Raman 780 nm

MNHNMNHN

� Historical context and

fluorescence characteristics

lead to a probable Ceylan

(Sri Lanka) origine

SOPRANO team SOPRANO team

Aknowledgments to

• Dominique DE LIGNY and Xiaochun WANG, LPCML, UCBL, Villeurbanne,France

• Clément MENDOZA, LPCML & LMPA, CEA Valhro-Marcoule, France

• Anne-Magali SEYDOUX-GUILLAUME, GET, UPS, Toulouse, France

• François FARGES, MNHN, Paris

Thanks for your attention !

Philosophy (…) established

as principle of things :

Water or abyss, dry

substance or atoms or

earth,

spirit or air, and in the

fourth place, light ;

Because these elements

distinguished each

other in the fact that

they cannot exchange

their nature but that

all – here more, there

less, here some of them

only – meet and

combine in a pleasant

manner.

La philosophie (…) a posé comme

principes des choses :

l’eau, ou abysse ; la substance

sèche, ou atomes, ou terre ;

l’esprit, ou air ; et, en quatrième

lieu, la lumière ;

car ces éléments se distinguent

en ce qu’ils ne peuvent

échanger leurs natures mais

que tous – ici davantage, là

moins, ici tous, là quelques-

uns seulement – se

rencontrent et s’associent de

manière heureuse.

De magia naturali,

Giordano Bruno,

1548-1600

philosopher, disciple of

Copernic, precursor of

modern science, burned

in Rome in 1600

2E

2T1

4A2

2T2

2A1

4T2

4T1

50

40

30

10

10 20 30

E/B

∆/BIntensité du champs crystallin

Energie

Cr3+

4A2

4T2

4T1

champ fort

2E

absorption

ra ie d’ém ission

bande de conduction

b ande de valence

Cr3+ in strong crystal field

2E

2T1

4A2

2T2

2A1

4T2

4T1

50

40

30

10

10 20 30

E/B

∆/BIntensité du champs crystallin

Energie

Cr3+

bande de conduction

b ande de valence

4A2

4T2

4T1

champ faible

2E

ba nde d’ém ission

absorption

Cr3+ in weak crystal field