Rare Earth-The Vitamins of Phosphors(Juestel PGS 2012)€¦ · To My PersonTo My Person Thomas...

Rare Earth Ions - The Vitamins of PhosphorsRare Earth Ions The Vitamins of Phosphors

Thomas Jüstel

S tt d l AZ M h 22nd 2012T. Jüstel, University of Applied Sciences Münster, Germany Slide 1

Scottsdale, AZ, March 22nd, 2012

To My PersonTo My PersonThomas Juestel (43), German, married

CV• University Bochum (1987 - 1994) Coordination Chemistry• Max-Planck Institute Mülheim (1995) ElectrochemistryMax-Planck Institute Mülheim (1995) Electrochemistry• Philips Research Aachen (1995 - 2004) Solid State Chemistry, Luminescence• University of Applied Sciences

Münster (since 2004) Functional optical materialsMünster (since 2004) Functional optical materials

Teaching• Inorganic Chemistry• Inorganic Chemistry

– Solid state chemistry– Coordination chemistry

• Material ScienceMaterial Science– Optical materials– Luminescent materials– Material characterisation

T. Jüstel, University of Applied Sciences Münster, Germany Slide 2

• Incoherent Light Sources https://www.fh-muenster.de/juestel

LiteratureLiterature• A.H. Kitai, Solid State Luminescence, Chapman & Hall, London (1993)

• G Blasse B C Grabmeier Luminescent Materials Springer Verlag Berlin• G. Blasse, B.C. Grabmeier, Luminescent Materials, Springer Verlag Berlin Heidelberg (1994)

• J.R. Coaton, A.M. Marsden, Lamps and Lighting, Arnold, London (1997)

• D.R. Vij, Luminescence of Solids, Plenum Press, New York and London (1998)

S Shi W M Y Ph h H db k CRC P (1999)• S. Shinoya, W.M. Yen, Phosphor Handbook, CRC Press (1999)

• A. Zukauskas, M.S. Shur, R. Caska, Introduction to Solid-State Lighting, John Wiley & Sons, Inc. (2002)

• E.F. Schubert, Light Emitting Diodes, Cambridge Univ. Press (2003)

• C.R. Ronda, Luminescence, Wiley-VCH (2008)

• T. Jüstel, S. Möller, H. Winkler, Luminescent Materials in Ullmann’sEncyclopedia of Technical Chemistry (2012)


AgendaAgenda1. Introduction to Phosphors1.1 What is luminescence?1.2 Luminescence processes1 3 Excitation mechanisms1.3 Excitation mechanisms1.4 Energy transfer1.5 Loss mechanisms

2. Rare Earth Ions2 1 Phosphors Activated by Rare Earth Ions2.1 Phosphors Activated by Rare Earth Ions2.2 Fundamental Aspects2.3 Issues in phosphor converted LEDs2.4 VUV Phosphors2.5 Future of Rare Earth Phosphors


What is Luminescence?What is Luminescence?• Definition

• Difference to incandescence

• Inorganic luminescent materials

• Role of physicists and chemists

• Application areas• Application areas


DefinitionDefinitionLuminescence is a process that corresponds to emission of electromagnetic radiation beyond thermal equilibriumradiation beyond thermal equilibrium.

Inorganic materials: Radiative recombination involving impurity levels:(a) conduction-band–acceptor-state transition(a) conduction band acceptor state transition(b) donor-state–valence-band transition(c) donor-acceptor recombination(d) bound-exciton recombination( )

ED

ED ED

EC

(b) (c) (d)(a)Eg Eg

EA

EgEg

EA


EV

Difference to IncandescenceDifference to IncandescenceIncandescence corresponds to emission from solids in thermal equilibrium „Black body radiation“, e.g. from incandescent lamps

Planck‘s law (1900)3

4x103

3000K

( )

2x103

3x103

3x103

2 nm-1

]

11

λcL T/c5

1e 2

c1 = 3.741832.10-16 Wm2

1 438786 10 2 K1x103

2x103

2000K

2500K

L e [W

m-21eλ T/c5 2

c2 = 1.438786.10-2 Km = Wavelength [m]Le = Spectral irradiance 0 200 400 600 800 1000 1200 1400 1600 1800 2000

5x102

2000K

Wavelength [nm]T = Temperature [K] Wavelength [nm]

Wien’s law

K]2880Tλ [T. Jüstel, University of Applied Sciences Münster, Germany Slide 7

K]μm2880Tλmax [

Inorganic Luminescent MaterialsLuminescent material = Host lattice + defects (+ dopants)

Inorganic Luminescent Materials

Host lattice Y2O3, Y3Al5O12, ZnS, Sr2Si5N8, …• Selection in accordance to requirements defined by the application:

excitation energy, absorption strength, chemical environment, temperature

Defects VK, VA, interstitials, ...• Afterglow (persistent luminescence)

L i hi ( t ti d th l hi )• Luminescence quenching (concentration and thermal quenching)– competitive absorption – energy transfer to defects + non-radiative relaxation

re absorption of emission– re-absorption of emission• Stability reduction

– formation of colour centres due to electron trapping

Dopants Cr3+, Mn4+, Sb3+, Pb2+, Eu2+/3+, Ce3+, ...• Selection and concentration depends on host lattice and application:

Solubility, mobility, oxidation state stability, CT state location


Solubility, mobility, oxidation state stability, CT state location• Co-dopants to enhance absorption

Inorganic Luminescent MaterialsHost lattice + Dopants (RE-, TM- and s2- ions)

ZH1 2

1

2 13 14 15 16 17

18

1

Inorganic Luminescent Materials

13B

5Be4

11Li3ZnH

14C

6

16O

8

15N

7

17F

9

18Ne10ZnHe2 13 14 15 16 17 1

2

312

39Sc21

40Ti

22

41V

23

42Cr24

43Mn25

44Fe

26

45Co27

46Ni28

47Cu

29

48Zn30

49Ga31Al

37K

19Na

50Ge

32Si

52Se34S

51As

33P

53Br35Cl

54Kr36Ar3 4 5 6 7 8 9 10 11 12 3

4

Mg

Ca20

38

La57Y

39

Hf72Zr40

Ta73Nb41

W74Mo42

Re75Tc43

Os76Ru44

Ir77Rh45

Pt78Pd46

Au79

Ag47

Hg80

Cd48

Tl81

In49

BaCs55Rb37

Pb82

Sn50

84Te

52

Bi83

Sb51

At85I

53

Rn86Xe54

Po8987

5

6

Sr38

56

88 104 105 106 107 108 109 110 111Ac89

RaFr87

788

Rf104

Db105

Sg106

Bh107

Hs108

Mt109

Ds110

Rg111

Ce58

Pr59

Nd60

Pm61

Sm62

Eu63

Gd64

Tb65

Dy66

Ho67

Er68

Tm69

Yb70

Lu71

Th90

Pa91

U92

Np93

Pu94

Am95

Cm96

Bk97

Cf98

Es99

Fm100

Md101

No102

Lr103

6

7


p

Inorganic Luminescent MaterialsInorganic Luminescent MaterialsRequirements on efficient phosphors

Hi hl t lli ti l• Highly crystalline particles• High purity (99,99% or better)• Homogeneous distribution of activator and sensitizer ions

ExcitationEmission

HeatHeat

Homogeneous distribution of activator and sensitizer ions

Absorption process related toHeat

S D

Absorption process related toOptical centres (impurities)• activators (A)

sensiti ers (S) ASET

D• sensitizers (S)• defects (D)• host lattice (band edge)

A

A AET

ETET

Energy transfer often occur prior to emission process!

A

H


Emission HeatHeat

Inorganic Luminescent MaterialsInorganic Luminescent MaterialsMorphology

• Nanoscale particles Molecular imaging, precursors• µ-sized particles Lamps, LEDs, CRTsµ p p , ,• Large single crystals Scintillators, LASERs• Ceramics LEDs, scintillators, LEDs

(cubic materials preferred)(cubic materials preferred)

1 10 100 1 10 100 1 101 nm 10 nm 100 nm 1 µm 10 µm 100 µm 1 mm 10 mm


Role of Physicists and ChemistsRole of Physicists and Chemists

Identify needs of specific application and translate into suitableIdentify needs of specific application and translate into suitablematerials taking physical/chemical processes into account:

– Excitation mechanisms– Energy transfer mechanisms– Emission mechanismsEmission mechanisms– Loss mechanisms– Stability

Saturation– Saturation– Colour point (shift)– Material preparation– Price and raw material access


Application AreasApplication AreasCRTs Plasma displaysLEDs

Fluorescent lamps EL DisplaysTomographs


Application AreasApplication Areas

Application Area ExamplesApplication Area Examples

Optical brightening Paint, pulp and paper, washing powder

Product protection Bills, stamps, credit cards, tickets, etc.

Emergency illumination Emergency exits and signs, runways

Advertisement illumination Ne discharge lamps

Medical imaging and treatment x-ray converter films, CTs, PETs Lamps for psoriasis and jaundice treatmentLamps for psoriasis and jaundice treatmentDental ceramics

Astronomy EUV/VUV-Amplifier

Biochemistry Labels for DNA, RNA, proteins

Lithography Photocopy machines


g p y py

Luminescence ProcessesLuminescence Processes

Type Excitation by Exampleyp y p

X-ray luminescence X-rays X-ray amplifierCathode luminescence Electrons (high U) CRTsCathode luminescence Electrons (high U) CRTs

Photo luminescence UV/Vis photons Fluorescent lampsElectro luminescence Electrical field (low U) LEDs EL displaysElectro luminescence Electrical field (low U) LEDs, EL displaysChemo luminescence Chemical reaction Emergency signalsBio luminescence Biochemical reaction Jelly fish, glow worms Thermo luminescence Heat Afterglow phosphorsThermo luminescence Heat Afterglow phosphors

Sono luminescence Ultra sound -M h l i M h i l P li tMechano luminescence Mechanical energy Peeling tape

Nature 455 (2008) 1089)Blue + UV + x-ray!


Excitation MechanismsExcitation MechanismsX-ray and high voltage electron excitation

1. Excitation of highly energetic core states

Primary electrons

core states2. Thermalization of electron-hole

pairs with band gap energy3 Energy transfer to activator [Xe]5d1

CBe- e- e-

3. Energy transfer to activator ions or centers

4. (Center) Luminescence

[Xe]5d

Ener

gy

Ban

d ga

p

Traps

Efficiency surprisingly well

[Xe]4f1Ce3+

EVB

Be-h+h+h+y p g y

understood, but with two different models:1 Robbins

Transfer Luminescence

Primary

Conversion


1. Robbins2. Bartram-Lempicki

Core bandPrimary

holes h+

Excitation MechanismsExcitation Mechanisms

1. Robbins

• Excitation with high energy particles• Energy used to create electron-hole pairs with band gap energyEnergy used to create electron hole pairs with band gap energy• Electron-hole pairs excite activators• = <h>/(Eg) . t

. qe. esc

– determined by host lattice, Eg by host lattice too– 1/(E ): proportional to photon yield or charge yield, also1/(Eg): proportional to photon yield or charge yield, also

important in direct conversion– t = N/(N+) (ratio capture by activator and defect centers)– = quantum efficiency of activator ion– qe = quantum efficiency of activator ion– esc = photon escape probability

D J Robbins On predicting the maximum efficiency of phosphor systems


D.J. Robbins. On predicting the maximum efficiency of phosphor systems excited by ionizing-radiation, J. Electrochem. Soc. 127 (1980) 2694


2. Bartram-Lempicki

• = . t . qe

2 5 independent of compo nds• 2.5 independent of compounds• Variations in scintillating efficiencies due to differences in

energy transfer efficiency (< 1) and band gap values• Important role of lattice excitation

R H B t d A L i ki Effi i f l t h l i d tiR.H. Bartram and A. Lempicki, Efficiency of electron-hole pair production in scintillators, J. Luminescence 68 (1996) 225



• Robbins description implies– Efficiently scintillating lattices– Efficiency is a lattice property– Scintillating efficiency decreases more than proportional onScintillating efficiency decreases more than proportional on

increasing ionicity (oxides), expressed in

• Bartram Lempicki description implies• Bartram-Lempicki description implies– Energy transfer lattice to activator determines efficiency– (almost) host lattice independent, generally assumed = 2.5– Oxidic (ionic) materials can be much more efficient than predicted

by Robbins



• Observations on X-ray and CRT phosphorsy p p

– Increasing covalency increases efficiency

– Small band gap desired

I ith hi d t h t i i ti– Issues with quenching due to photoionisation

– Lattice defects cause undesired afterglow


Excitation MechanismsExcitation MechanismsVUV (EUV) excitation

CB

Excitation energy > EG of the host lattice Band gap excitation

Eg

Trap

transfer

A*

A+

Eg

A

QE QE * k /(k k ) *

VB

QE = QEA* transfer = kr/(kr + knr) * transfer

Crystallinity (defect density) has strong


Crystallinity (defect density) has strong impact on VUV efficiency and afterglow

Excitation MechanismsExcitation MechanismsPenetration depth of VUV radiation

Absorption 1,0125 nm excitation

Emission spectra of (Y,Gd)BO3:Eu are dependent on local symmetry

by activator

0 6

0,8 160 nm excitation

230 nm excitation

sity

[a.u

.]

Absorption by host lattice

0,4

0,6

Em

issi

on in

ten

by host lattice

590 600 610 620 6300,0

0,2

E

W l th [ ] /

230 nm exc. x = 0.638, y = 0.360 10 kV electrons (~400 nm) x = 0.637, 0.362160 nm exc. x = 0.646, y = 0.349 2 kV electrons (~30 nm) x = 0.644, 0.350

Wavelength [nm] Penetration depth = 0.046*U5/3/ [µm]


Band gap excitation penetration depth < 100 nm

Excitation MechanismsEmission spectra of BaMgAl10O17:Eu2+ as function of penetration depth

Excitation Mechanisms

1,0

ensi

ty

Excitation at 147 nm1,0 BaMgAl10O17:Eu2+

0,6

0,8

em

issi

on in

te Excitation at 172 nm

Excitation at 254 nm 0,6

0,8 Ba0.75Al11O17.25:Eu2+

0,2

0,4

Nor

mal

ised

e

0,2

0,4

400 450 500 550 6000,0

N

Wavelength [nm]400 450 500 550 600

0,0

Wavelength [nm]

BAM:Eu surface suffers from MgO lack formation of Ba1-xAl11O17.5-x:Eu

(Improved BaMgAl10O17:Eu,(Mn) by application of Mg2+


( p g 10 17 ( ) y pp gexcess during synthesis, J.-P. Cuif, Rhodia, PGS 2005)

Excitation MechanismsExcitation MechanismsExcitation by UV or visible radiation

Excitation energy < EG of the host lattice Excitation of optical centres

activator excitation sensitiser excitation

A*A*

CBS*A**

CB

k

A*Transfer

k knrA

VBS

VBA

kr

QEA = kr/(kr + knr) = /0 QE = QEA * Transfer


with kr + knr = 1/ and kr = 1/0

Excitation MechanismsExample: BaMgAl10O17 doped by 10% Eu2+

Excitation Mechanisms

80 0

100,0Host lattice

Reflection spectra Emission and excitation spectra1,0

4f65d1 - 4f7Host lattice4f7 - 4f65d1

60,0

80,0

ectio

n [%

]

0,6

0,8

Inte

nsity

20,0

40,0

Eu2+

4f7 - 4f65d1

Ref

le

0,2

0,4

Rel

ativ

e

100 200 300 400 500 600 700 8000,0

Wavelength [nm]100 200 300 400 500 600 700 800

0,0

Wavelength [nm]

• Host lattice VB CB 180 nm (7.0 eV)• Eu2+ [Xe]4f7 [Xe]4f65d1 250 nm (5.0 eV) and 310 nm (4.0 eV)• Allowed transition Intense absorption bands and fast decay (~1 µs)


Allowed transition Intense absorption bands and fast decay ( 1 µs)

Excitation MechanismsExcitation MechanismsExample: BaMgAl10O17 doped by 5% Mn2+

1,0 1,0

Mn2+

Reflection spectra Emission and excitation spectra

80 0

100,0Host lattice

Mn2+

3d5 3d5

0,6

0,8

0,6

0,83d5 - 3d5

e in

tens

ity

60,0

80,0

M 2+

3d - 3d

ectio

n [%

]

0,2

0,4

0,2

0,4

Rel

ativ

e

20,0

40,0Mn2+

3d5 - 3d5

Ref

le

100 200 300 400 500 600 700 8000,0 0,0

Wavelength [nm]100 200 300 400 500 600 700 800

0,0

Wavelength [nm]

• Host lattice VB CB 180 nm (7.0 eV)• Mn2+ [Ar]3d5 [Ar]3d5 200 nm (6.2 eV) and 450 nm (2.8 eV)• Forbidden transition Weak absorption bands and slow decay (~10 ms)


• Forbidden transition Weak absorption bands and slow decay (~10 ms)

Excitation MechanismsExcitation MechanismsExample: LaPO4 doped by 20% Ce3+

100,0

1,0

Ce3+

5d1 4f1

Emission and excitation spectraReflection spectra

60,0

80,0

ctio

n [%

]

Host Lattice 0,6

0,8

tens

ity

5d1 - 4f1

20,0

40,0

R

efle

c

C 3+0,2

0,4

Rel

ativ

e In

t

200 300 400 500 600 700 8000,0

Wavelength [nm]

Ce 4f1-5d1

200 300 400 500 600 700 8000,0

Wavelength [nm]

• Host lattice VB CB 150 nm (8.2 eV)• Ce3+ [Xe]4f1 [Xe]5d1 200 nm (6.2 eV) and 450 nm (2.8 eV)• Allowed transition Intense absorption bands and fast decay (~ 30 ns)


Allowed transition Intense absorption bands and fast decay ( 30 ns)

Excitation MechanismsExcitation MechanismsExample: Y2O3 doped by 5% Eu3+

Emission and excitation spectraReflection spectra100

7F0 - 5DJ

Band gap

1,05D0 -

7FJ

Band gap

Charge-Transfer

60

80

ectio

n [%

]

0,6

0,8

nten

sity

20

40

Ref

le

Charge-0,2

0,4

7F0 - 5D2

7 5

Rel

ativ

e in

200 300 400 500 600 700 8000

Charge-Transfer

150 200 250 300 350 400 450 500 550 600 650 700 7500,0

7F0 - 5D1

7F0 - 5D3

Wavelength [nm]

• Host lattice VB CB 210 nm (5.9 eV)• Eu3+ Charge transfer 230 nm (5.4 eV)

[Xe]4f6 [Xe]4f6 395 nm (3.1 eV) and 465 nm (2.2 eV)


[Xe]4f [Xe]4f 395 nm (3.1 eV) and 465 nm (2.2 eV)• Forbidden transitions Weak absorption bands and slow decay (~3 ms)

Excitation MechanismsExcitation MechanismsSensitisation

3dn - 3dn and 4fn - 4fn transitions of are very weak

Ways to enhance absorption CT levely p• Involvement of allowed transitions

– Charge-transfer (CT) of Eu3+

– 4fn – 4fn-15d1 levels (Tb3+, Eu2+, Ce3+) 5D

CT level

relaxation( )

• Sensitisation (Energy Transfer)– Ce Tb

5D0

– Pr Tb– Nd Gd– Pr Gd

7F– Bi Eu– ….

7FJ

Simplified energylevel scheme of Eu3+


level scheme of Eu

Energy Transfer (ET)Energy Transfer (ET)Requirements

• Sensitiser ion and the activator ion have to show physicalinteraction:– Coulomb interaction– Exchange interaction

• Spectral overlap (conservation of energy)


Energy TransferEnergy TransferThe probability PET for energy transferis given by the following term:is given by the following term:

PET = (2/ħ).() < i | H | f >²

i: Wave function of the initial statef: Wave function of the final statefH: Operator coupling the states: Spectral overlap (energy conservation)

Spectral overlap

= g (E) g (E) dE = gS(E).gA(E).dE

gS(E) and gA(E): Normalised optical line shapef ti f iti d ti t i


functions for sensitiser and activator ions

Energy TransferEnergy TransferCorresponds to

E i ti• Energy migration • Concentration quenching• Thermal quenchinge a que c g• Cross relaxation• Sensitization schemes

Some rules• ET from a broad band emitter to a line emitter only possible forET from a broad band emitter to a line emitter only possible for

nearest neighbor in the host lattice (Ce3+ - Tb3+)• ET from a line emitter to a band absorber proceeds over long

distances (Gd3+ Ce3+)distances (Gd3+ - Ce3+)• ET strongly depends on average distance and thus

concentration of luminescent centers


Energy TransferExample: Ce3+ and Tb3+ doped LaPO4

1,0 Tb3+ 4f5d b ti

Tb3+ 4f4f emission

Energy Transfer

LaPO4:TbTb3+ (Tb3+)** Absorption 4f - 5d(Tb3+)** (Tb3+)* Relaxation to 4f level

0,6

0,8

, Tb3 4f5d absorption

sity

(a.

u.)

Tb 4f4f emission

(Tb ) (Tb ) Relaxation to 4f level(Tb3+)* Tb3+ Emission 4f - 4f

200 300 400 500 600 700 8000,0

0,2

0,4

Inte

n

LaPO4:Ce,TbCe3+ (Ce3+)* Absorption 4f - 5d Tb3+ absorption

Tb3+ 4f4f emission

200 300 400 500 600 700 800Sample V1377

Wavelength [nm]

Ce (Ce ) Absorption 4f 5d(Ce3+)* + Tb3+ Ce3+ + (Tb3+)* ET from Ce to Tb(Tb3+)* Tb3+ Emission 4f - 4f

0,6

0,8

1,0p

Ce3+ absorption

sity

(a.u

.)

Efficiently excited by 254 nm radiation!200 300 400 500 600 700 800

0,0

0,2

0,4

Inte

ns


200 300 400 500 600 700 800Wavelength [nm]

Energy TransferExample: BaMgAl10O17:Eu co-doped by transition metal ions

Energy Transfer

UV

1

Energy Transfergy

2

Divalent RE ions Ba2+ sites in the conduction layer Eu2+, Yb2+

Divalent TM ions tetrahedral gaps in the spinel blocks Mn2+, Co2+

Trivalent TM ions octahedral gaps in the spinel blocks Cr3+ Ti3+


Trivalent TM ions octahedral gaps in the spinel blocks Cr3+, Ti3+

Energy Transfer

E i i t Light outputExample: BaMgAl10O17:Eu2+ co-doped by Mn2+

Energy Transfer

0,8

1,0 BAM-I:0.05Mn BAM-I:0.10Eulow Mn BAM-I:0.10EumediumMnBAM-I:0 10EuhighMn

y

0,8

1,0

-R)

Emission spectra Light output

0,6

0,8 BAM-I:0.10EuhighMn

ativ

e in

tens

ity

0,6 BAM-I:0.05Mn BAM-I:0.1EumediumMnBAM-I:0 1EuhighMn

LO =

QE*

(1-

0,2

0,4

Rel

a

0,2

0,4 BAM-I:0.1EuhighMn

Ligh

t out

put

300 350 400 450 500 550 6000,0

Wavelength [nm]150 200 250 300 350

0,0

LWavelength [nm]

• Efficient energy transfer from Eu2+ to Mn2+

• Eu2+ improves VUV efficiency of Mn2+ doped BaMgAl10O17• High Mn2+ concentration reduces VUV efficiency of BaMgAl10O17:Eu Mn


High Mn concentration reduces VUV efficiency of BaMgAl10O17:Eu,Mn

Energy TransferEnergy pathways in BaMgAl10O17:Eu,Mn

Energy Transfer Energy pathways in BaMgAl10O17:Eu,Mn

Conduction Band

172 nm

eV m)

254 nm[Ar]3d5*

gy

Eatio

n172 nm

[Xe]4f65d1

[Ar]3d5M 2+E

g=

7.0

(~ 1

80 n

m

515 nm370 nmEne

rg

Em

ission

UV

Exc

it

453 nmMn2+E (

VU

[Xe]4f7

Eu2+

Valence BandEu


Energy Transfer and Cross RelaxationEnergy Transfer and Cross Relaxation• Cross relaxation responsible for

th hi f l ithe quenching of luminescenceof higher 4f levels of Tb3+ at ahigh Tb3+ concentration

• Cross relaxation also for Eu3+,Sm3+ , Pr3+, and Dy3+

• Relaxation to the first excitedstate can be promoted by high-energy photons tooenergy photons too


Loss MechanismsLoss Mechanisms1. The absorbed energy does not reach the activator ion (transfer)

a) Competitive absorption) p pb) ET to defects or non-luminescent impurity ionsc) Excited state absorptiond) Auger processes

2. The absorbed energy reaches the activator ion, but non-radiative (act)channels exists at the cost of radiative return to the ground statea) Crossing of excited and ground state parabola (tunneling)a) Crossing of excited and ground state parabola (tunneling)b) Multi-phonon relaxationc) Cross-relaxationd) Photoionisation)e) Energy transfer to quenching sites = f(T)

3. Emitted radiation is re-absorbed by the luminescent material (esc)a) Self-absorption due to spectral overlap between excitation and emission bandb) Additional absorption bands due to degradation of the material,

b l t f ti


e.g. by colour centre formation

Loss MechanismsRelated to the host lattice and host lattice activator interaction

Loss Mechanisms

CB

Internal Quantum EfficiencyIQE = act

= r/(r + nr)

A*

CB r (r nr)= /0

(Anti proportional to decay time)abs

A

Egtransfer External Quantum Efficiency

EQE = Nh(emitted)/N h(absorbed)= transfer* act* esc

act esc

A

VB

A+

transfer act esc(No correlation to decay time!)

Light YieldLight YieldLY = EQE * abs = EQE*(1-R )(No correlation to decay time!)


Loss MechanismsLoss MechanismsRelated to the activator ions (center luminescence)

Relevant quenching mechanisms

a) Tunneling to the ground state (direct)) g g ( )• Stokes Shift = Energy distance between

absorption and emission bandS = Sehwe + Sghwgg g

• FWHM ~ S• Thermal quenching increases with

increasing Dr = re – rg andDr depends on activator-host latticeinteraction

b) Tunneling to the ground state via a low-lying CT state


c) Photoionisation to CB

Loss Mechanisms1. Weak to no electron-phonon-coupling• High IQE, EQE determined by ET processes

Loss Mechanisms

g y• Thermal quenching mainly due to photoionisation• 4f 4f transitions (shielded 4f-shell: small CFS)• Lines Eu3+, Tb3+, ….

2. Moderate electron-phonon-coupling• High to moderate IQEg• Thermal quenching due to tunneling or

photoionis.• 4f 5d transitions (large CFS)• Narrow bands Eu2+ Ce3+• Narrow bands Eu2+, Ce3+, ….

3. Strong electron-phonon-couplingg p p g• High to low IQE at RT, strong thermal quenching• Thermal quenching mainly due to tunneling• ns2 ns1np1 or CT transitions

Broad bands Pb2+ Bi3+


• Broad bands Pb2+, Bi3+, ….

Loss MechanismsStrong electron-phonon-coupling

E l L i f Pb2+ [X ]4f145d106 2 [X ]4f145d106 16 1

Loss Mechanisms

1,0 Excitation

1,0 Excitation

y 1,0 Excitation

BaSi2O5:Pb Sr2MgSi2O7:Pb SrLaBO4:Pb

Example: Luminescence of Pb2+ - [Xe]4f145d106s2 [Xe]4f145d106s16p1

0,6

0,8

Emission

ssio

n in

tens

ity

0,6

0,8

Emission

mis

sion

inte

nsity

0,6

0,8

Emission

ssio

n in

tens

ity

0,2

0,4

orm

aliz

ed e

mis

0,2

0,4

Nor

mal

ized

em

0,2

0,4

Nor

mal

ized

em

i

250 300 350 400 450 500 550 6000,0

N

Wavelength [nm]

250 300 350 400 450 500 550 6000,0

Wavelength [nm]250 300 350 400 450 500 550 600

0,0

N

Wavelength [nm]

Phosphor Stokes Shift [cm-1] FWHM [cm-1] EQE [%]BaSi2O5:Pb 10600 2700 90Sr2MgSi2O7:Pb 12000 4300 75


Sr2MgSi2O7:Pb 12000 4300 75SrLaBO4:Pb 17700 5300 65

Loss MechanismsStrong electron-phonon-coupling

E l L i f Pb2+ [X ]4f145d106 2 [X ]4f145d106 16 1

Loss Mechanisms

50000

60000

BaSi2O5:Pb (NP808-03) NP80803025C NP80803075C NP80803150CNP80803200C

nts]

0,8

1,0

BaSi2O5:Pb (NP808-03)

sity

Example: Luminescence of Pb2+ - [Xe]4f145d106s2 [Xe]4f145d106s16p1

20000

30000

40000

NP80803250C NP80803300C NP80803330C

sion

inte

nsity

[Cou

0,4

0,6

0,8

y = A2 + (A1-A2)/(1 + exp((x-x0)/dx))Chi^2/DoF = 0.00003R^2 = 0.99827 A1 0.99596 ±0.0039A2 0 0

ive

emis

sion

inte

ns

300 350 400 450 5000

10000

20000

Em

iss

Wavelength [nm]

254 nm excitation0 50 100 150 200 250 300 350

0,0

0,2

A2 0 ±0x0 375.36752 ±2.97042dx 52.20839 ±2.74147

integral I350nm

Rel

ati

Temperature [°C]

254 nm excitationh

Wavelength [nm] Temperature [ C]

4000

5000

6000

7000

q r

po

n

ml

k

j

i

h

g

fe

db

a

cm-1]

Correlation betweenFWHM and Stokes Shift for s2-ion

0

1000

2000

3000

ic

FWH

M [c

activated phosphorsQuenching due totunneling to the


0 5000 10000 15000 20000

0

Stokes shift [cm-1]ground state

Loss MechanismsLoss MechanismsPhotoionisation

• Excited An+ ion ionisesCB

• Released electron is retrapped, e.g. by anion vacancies

(An+)*g y

• Causes afterglowScintillatorsAn+

Eg– Scintillators– Persistent phosphors

An+

VB


Rare Earth IonsRare Earth Ions


Rare Earth Ions – Vitamins?Vitamins are organic molecules that are needed in small amountsin the diets of higher animals to maintain all metabolic functions

Rare Earth Ions Vitamins?

Higher animals Advanced phosphors

~ 12 Vitamins 12 Rare earth ions

A B1 B2 B3 Ce3+ Pr3+ Nd3+ Sm2+/3+A, B1, B2, B3, Ce , Pr , Nd , Sm ,B6, B12, B13, C, Eu2+/3+, Gd3+, Tb3+, Dy3+,D, E, H, K Ho3+, Er3+, Tm3+, Yb2/3+

Low concentrations required Low doping levelsmg – g / day 0.1 – 5 atom-%


Rare Earth IonsLanthanides originates from the Greek word “λανθανειν”,

which means “to lie hidden”

Rare Earth Ions

1 18

Groups

B5

Be4

Li3ZnH

1

C6

O8

N7

F9

Ne10ZnHe2

2 13 14 15 16 17 1

2

Sc21

Ti22

V23

Cr24

M25

F26

C27

Ni28

C29

Z30

G31Al13BBe

K19Na11Li

G32

Si14C

S34S

16O

A33P

15N

Br35Cl17F

K36Ar18Ne

3 4 5 6 7 8 9 10 11 12 3

4

Mg12

Ca20

57Y

39Sc

72Zr40Ti

73Nb41V

74Mo42Cr

75Tc43Mn

76Ru44Fe

77Rh45Co

78Pd46Ni

79

Ag47Cu

80

Cd48Zn

81

In49Ga

55Rb37K

82

Sn50Ge

84Te

52Se

83

Sb51As

85I

53Br

86Xe54Kr 4

5

6

Ca

Sr38

56La Hf Ta W Re Os Ir Pt Au Hg TlBaCs Pb Bi At RnPo

Ac89

RaFr87

6

788

Rf104

Db105

Sg106

Bh107

Hs108

Mt109

Ds110

Rg Cn111 112

Ce58

Pr59

Nd60

Pm61

Sm62

Eu63

Gd64

Tb65

Dy66

Ho67

Er68

Tm69

Yb70

Lu71

90 91 92 93 94 95 96 97 98 99 100 101 102 103

6


Th90

Pa91

U92

Np93

Pu94

Am95

Cm96

Bk97

Cf98

Es99

Fm100

Md101

No102

Lr103 7

Rare Earth IonsInstead of “to lie hidden” λανθανειν,

a better name would be “to be outstanding” επιφανης – epifanides

Rare Earth Ions

g φ ης p(A. Meijerink, PGS 2011)


Phosphors Activated by Rare Earth IonsPhosphors Activated by Rare Earth IonsCathode-ray tubes Early phosphors Recent phosphors

Z S A Z S AZnS:Ag ZnS:AgZnS:Cu,Al,Au ZnS:Cu,Al,Au(Zn,Cd)S:Ag YVO4:Eu(Zn,Cd)S:Ag YVO4:EuZn3(PO4)2:Mn Y2O2S:Eu

Fluorescent lampsMgWO4 BaMgAl10O17:EuMgWO4 BaMgAl10O17:EuZn2SiO4:Mn LaPO4:Ce,Tb

CeMgAl11O19:TbGdMgB5O10:Ce,Tb

(Zn,Be)2SiO4:Mn Y2O3:EuCa (PO ) (F Cl):Sb Mn GdMgB O :Ce Tb Mn


Ca5(PO4)3(F,Cl):Sb,Mn GdMgB5O10:Ce,Tb,Mn

Phosphors Activated by Rare Earth Ions

Activator Host Lattice Emission at [nm] Colour Application

Phosphors Activated by Rare Earth Ions

Ce3+SrAl12O19

LaPO4

YPO4

300320

335, 355

UV-BUV-BUV-A

Tanning lamps

Pr3+ Gd2O2S CaTiO3

510610

GreenRed

CT ScannerFEDs

Nd3+ Y3Al5O12 1064 Red Laser

Sm3+ Y3Al5O12 620 Red Laser

Eu2+SrB4O7

Sr4Al14O25

368490

UV-ABlue

Black light lampsAfterglow

CaS 655 Rot LEDs

Eu3+ (Y,Gd)BO3

YVO4

611615

RedRed

Plasma displaysHP Hg discharge lamps

Gd3+ (L Bi)B O 311 UV B P i i lGd3+ (La,Bi)B3O6 311 UV-B Psoriasis lamps

Tb3+ Y2SiO5

(Y,Gd)BO3

Gd2O2S

544544544

GreenGreenGreen

Projection TV setsPlasma displaysX-ray converter screens


Yb3+ Y3Al5O12 620 Red Laser

Rare Earth Ions – Fundamental AspectsRare Earth Ions Fundamental AspectsElectron configuration of rare earth metals and ions

Metals[Xe] La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu6s 2 2 2 2 2 2 2 2 2 2 2 2 2 2 25d 1 0 0 0 0 0 0 1 0 0 0 0 0 0 14f 0 2 3 4 5 6 7 7 9 10 11 12 13 14 14

IIons[Xe] La3+ Ce3+ Pr3+ Nd3+ Pm3+ Sm3+ Eu3+ Gd3+ Tb3+ Dy3+ Ho3+ Er3+ Tm3+ Yb3+ Lu3+

Ce4+ Pr4+ Nd4+ Sm2+ Eu2+ Tm2+ Yb2+

4f 0 1 2 3 4 5 6 7 8 9 10 11 12 13 144f 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14

Example ml -3 -2 -1 0 1 2 3 -2 -1 0 1 2 0 -1 0 1

Gd3+/Eu2+ Gd3+/Eu2+

S = s = 7/2 2S+1 = 8 strongly paramagnetic ions

4f 5d 6s

6p


S s 7/2 2S+1 8 strongly paramagnetic ionsL = |l| = 0 „S“ LS-Term symbol 8S

Rare Earth Ions – Fundamental Aspects

History of distangling the energy level structure

Rare Earth Ions Fundamental Aspects

1908 Bequerelsharp lines in optical spectra of lanthanide ionssharp lines in optical spectra of lanthanide ions

1937 Van VleckThe puzzle of rare earth

1960’s Judd Wybourne Dieke Carnall1960’s Judd, Wybourne, Dieke, CarnallTheory for energy level structure and transition probabilities of 4f-4f transitions p


Rare Earth Ions – Fundamental AspectsEnergy level structure of [Xe]4fn ionsPartly filled 4f shell results in multiple electron configurations:


Partly filled 4f-shell results in multiple electron configurations:e.g. Tb3+ 4f8 → 8 electrons into 7 f-orbitals: 3003 different arrangements!

Free ion energy levels due to:1. Electrostatic interactions (comparable to 3dn ions)2 S i bit li (l th f 3dn i )2. Spin-orbit coupling (larger than for 3dn ions )3. Crystal field splitting (smaller than for 3dn ions)

Ground state ml = -3 -2 -1 0 1 2 3 7F6

4f

1st excited state ml = -3 -2 -1 0 1 2 3 5D4


4f

Rare Earth Ions – Fundamental AspectsTypical emission spectrum of Tb3+ (LuAG:Tb)


Characteristic luminescence of lanthanides- Sharp emission lines- Almost independent of chemical environment, e.g. green-yellow emission of Tb3+ phosphors


e.g. green yellow emission of Tb phosphors- High quantum yield (> 90%), due to small Stokes shift

Rare Earth Ions – Fundamental AspectsRare Earth Ions Fundamental Aspects4f75d1

Line emitting ions

Simplified energy level schemes of selected RE ions254 nm

4f65d1

4.0x1045d1

4f72p-1

6P7/2

6I7/2

Line emitting ionsPr3+

Nd3+

Sm2+/3+3.5x104

5D3m-1

] 5D3

7/2

Eu3+ (Eu2+)Gd3+

Tb3+

Dy3+

3.0x104

2.5x104

nerg

y[c 5D2

5D15D0

5D4

DyHo3+

Er3+

Tm3+

3

2.0x104

1.5x104

En

7F 2 10

Yb3+

Band emitting ionsCe3+

1.0x104

0.5x104

Eu3+

5 423

1 00.0 8S7/2

2F7/2

2F5/2

7F6

Eu2+Ce3+ Gd3+ Tb3+

54

23

7F68S7/2

CePr3+

Nd3+

Eu2+

2


4f6 4f74f1 4f7 4f8 Yb2+[Xe]

Rare Earth Ions – Fundamental Aspects1. Electrostatic interactions


Shielding due to inner electrons described by the so-called Slater parameters (compare to Racah parameters)p ( p p )

Electrostatic interaction increases with effective charge on ect ostat c te act o c eases t e ect e c a ge othe activator ion (charge density)Therefore splitting between different terms depends on • Oxidation state• Nucleus charge• Charge flow back from ligands (polarisibility of anions)


Charge flow back from ligands (polarisibility of anions)

Rare Earth Ions – Fundamental AspectsRare Earth Ions Fundamental Aspects2. Spin-orbit coupling

Spin-orbit coupling constant ζ increases through the lanthanide series, i.e. from ζ(Ce) = 650 cm-1 to ζ(Yb) = 2930 cm-1

Further splitting of LS terms into J-levels by energy assuming weak spin-orbit coupling:energy, assuming weak spin-orbit coupling:

Complete term symbol:

2S+1LJ with |L-S| < J < L+S

For Tb3+ Ground state: 7F6,5,4,3,2,1,0Excited state: 5D4,3,2,1,0


Rare Earth Ions – Fundamental AspectsRare Earth Ions Fundamental Aspects3. Crystal-field splitting

Further splitting of J multiplets into a maximum of 2J+1 levelsCrystal field splitting ~ 100 cm-1 + sensitive function of site symmetry

2,00

LuAG:Nd3+

4F3/2 – 4I11/21

1,25

1,50

1,75

[a.u

.]

∆E = 203 cm-1

six levels without external magnetic

0,50

0,75

1,00

Inte

nsity

[

external magneticfield Dodecahedral coordination1000 1010 1020 1030 1040 1050 1060 1070 1080 1090 1100

0,00

0,25

Wavelength [nm]

Extra fitting parameters Bkq for fit of experimentally observed levels:


Rare Earth Ions – Fundamental AspectsRare Earth Ions Fundamental AspectsIn summary: RE ions exhibit a large number of energy levels 2S+1LJ

Early experimental and theoretical work on LaCl3:Ln3+ and LaF3:Ln3+ by Dieke and Carnall (experiment) and Judd, Crosswhite, Wybourne (theory): “Dieke diagram” and the “Blue book”


g

Rare Earth Ions – Fundamental Aspects

Gerhard H. Dieke 1968



Rare Earth Ions – Fundamental AspectsEnergy levels of trivalent lanthanides: Dieke diagram



Rare Earth Ions – Fundamental AspectsA. Meierjink: Extended Dieke diagram


T. Jüstel, University of Applied Sciences Münster, Germany Slide 63P.S. Peijzel, A. Meijerink, R.T. Wegh et al, J. Solid State Chem. 178 (2005) 448.

Rare Earth Ions – Fundamental AspectsComplete energy level diagram


Ce3+ ~ Yb3+

Pr3+ ~ Tm3+

Nd3+ ~ Er3+Nd ErPm3+ ~ Ho3+

Sm3+ ~ Dy3+

Eu3+ ~ Tb3+Eu3 ~ Tb3

Gd3+

E l l litti iEnergy level splitting increasesfrom Ce3+ to Yb3+ due to increasing nucleaus charge


Fundamental Aspects – 4f-4f TransitionsCharacteristic optical properties

Fundamental Aspects 4f 4f Transitions

1) Sharp lines (atomic like), Stokes shift ~ 0 cm-1

2) Little influence of environment on energy level scheme

3) Parity forbidden transitions (~ms life time, f ~10-5)) y ( , )

Origin: Shielding of 4fn electrons by outer filled 5s and 5p shellsby outer filled 5s and 5p shells→ no shift of excited state parabola and strong zero-phonon lines (ZP)


Fundamental Aspects – 4f-4f TransitionsExample: Eu3+ - Typical excitation and emission spectra (Y2SiO5:Eu)

Fundamental Aspects 4f 4f Transitions 1,0

Charge-Transfer

0,6

0,8

inte

nsity

[a.u

.]

0,2

0,4

7F0 - 5D4

7F0 - 5L6

7F0 - 5D1

7F0 - 5D3

7F0 - 5D2

Em

issi

on i

100 150 200 250 300 350 400 450 500 550 6000,0

Wavelength [nm]

1,0

5D0 -7F2

0,6

0,8

n in

tens

ity [a

.u.]

5D0 -7F4

0 0

0,2

0,4

Em

issi

on

5D0 - 7F0

5D0 -7F1

5D0 -7F3

0 4


500 550 600 650 700 750 8000,0

Wavelength [nm]

Fundamental Aspects – 4f-4f TransitionsEmission spectra and colour points of Eu3+ activated phosphorsFundamental Aspects 4f 4f Transitions

5D0 - 7F3

5D0 - 7F4

5D0 - 7F2

5D0 - 7F1

(Y Gd)BO E

Phosphor CIE1931 colour pointx y

(Y,Gd)BO3:Eu

Y2O3:Eu

ät

(Y,Gd)BO3:Eu 0.640 0.360

YVO4:Eu

Inte

nsitä Y2O3:Eu 0.641 0.344

YVO E 0 645 0 343Y2O2S:Eu

YVO4:Eu 0.645 0.343

Y2O2S:Eu 0.650 0.342

Colour saturation: Y O S:Eu > YVO :Eu > Y O :Eu > (Y Gd)BO :Eu

600 650 700 750

Wellenlänge [nm]Y2O2S:Eu 0.650 0.342


Colour saturation: Y2O2S:Eu > YVO4:Eu > Y2O3:Eu > (Y,Gd)BO3:Eu

Fundamental Aspects – 4f-4f Transitions

Observed emission spectrum due to4f 72p-14.0x104

Fundamental Aspects 4f 4f Transitions Emission spectra and colour points of Eu3+ activated phosphors

Observed emission spectrum due to5D0 7FJ transitions (lines)4f 65d

3.0x104

3.5x104

[cm

-1]

a) Inversion symmetry (S6, D3d)Magnetic dipole transitions, e.g. 5D0 - 7F1J = 0, ± 1 (J = 0 J = 0 forbidden)

4

2.5x104

e nu

mbe

r

( )MeBO3:Eu (Calcite, Vaterite) ~ 8 - 16 ms

5D3

5D25D15D0

1.5x104

2.0x104

Wav

b) No inversion symmetryElectric dipole transitions 5D0 -7F2,4

( )7F6

5

5.0x103

1.0x104

J 6 (Ji = 0 Jf = 2, 4, 6)Y2O3:Eu (Bixbyite), Y(V,P)O4:Eu (Xenotime) ~ 2 - 5 ms

Eu3+ Eu2+

54

2 310

8S7/20.0


Eu4f6

Eu4f7

Fundamental Aspects – 4f-4f Transitions0,9

1,0Sample: Y2O3:Eu3+ (U770)

00 K

]

3,5x106

4,0x106

Ex= 254 nmslit size: Ex = 4.00 nm, Em = 1.00 nm

Sample: Y2O3:Eu3+ (U770)

100.0 K 150.0 K200 0 K

Fundamental Aspects 4f 4f Transitions

0 4

0,5

0,6

0,7

0,8

[nor

mal

ised

to 1

0

2,0x106

2,5x106

3,0x106

nsity

[cps

]

200.0 K 250.0 K 300.0 K 350.0 K 400.0 K 450.0 K 500.0 K

0 0

0,1

0,2

0,3

0,4

Inte

gral

inte

nsity

Integrated IntensityEx= 254 nmTQ= K

0 0

5,0x105

1,0x106

1,5x106

Inte

n

Y O E (5%)

100 125 150 175 200 225 250 275 300 325 350 375 400 425 450 475 5000,0

T [K]500 550 600 650 700 750

0,0

Wavelength [nm]

10000

Sample: Y2O3:Eu3+ (U770)

Ex= 254 nm T=100.00 KT 150 00 KY2O3:Eu(5%)

exc = 254 nmem = 611 nm 100

1000

ty [c

ount

s]

T=150.00 K T=200.00 K T=250.00 K T=300.00 K T=350.00 K T=400.00 K T=450.00 Kem 611 nm

QE ~ 95%1/e = 1.1 ms, 1/10 = 2.5 ms

1

10In

tens

it T=500.00 K


TQ1/2 > 500 °C 0 2 4 6 8 10 12 14 16 18 201

time [ms]

Fundamental Aspects 4fn4fn-15d1 TransitionsFundamental Aspects 4f 4f 5d TransitionsCe3+ Eu2+[Xe]4f1 [Xe]5d1 [Xe]4f7 [Xe]4f65d1

60 60

cm-1

]

50

40

2DJ

cm-1

]

50

40

rgy

[103

c

30

40

rgy

[103

c

30

40

6

6I7/2

6D9/2 8HJ

Ene

r

20 Ene

r

20

6P7/2

2F

10 10


2F5/2

2F7/20 0 8S7/2

Fundamental Aspects 4fn4fn-15d1 TransitionsExample: Ce3+ luminescence in different inorganic host lattices

Fundamental Aspects 4f 4f 5d Transitions Ce3+

conduction band edge

4

6

5d-level 2F7/2-state

ground state 2F5/2

valence band edge

Some observationsYAG:Ce and LuAG:Ce are efficientphosphors with a high thermal

2

E [e

V]

p p gquenching temperature

YGG:Ce and LGG:Ce suffer from

-2

0

ener

gy

thermal quenching

Y2O3:Ce does not luminesce at all

YAG LuAG YGG Y2O3 CaS MgS CaO LiSrAlF6

-6

-4

?

MgS:Ce and CaS:Ce are efficientEL phosphors

Quenching by multiphonon relaxation? Nocross-relaxation? Not li ? Y f l S S Gd Al O C

2 3 g 6

host material?


tunneling? Yes for a large S.S.: Gd3Al5O12:Cephotoionisation? Yes for small [Xe]4f65d1 to CB distance

Fundamental Aspects 4fn4fn-15d1 Transitions250000

Sample: Y3Al5O12:Ce3+

250.0 K 275 0 K 0 9

1,0TQ50= 530 K (257 °C)

Data: DataYAG IntNorm

Fundamental Aspects 4f 4f 5d Transitions

150000

200000

nts]

275.0 K 300.0 K 325.0 K 350.0 K 375.0 K 400 0 K 0 6

0,7

0,8

0,9 Data: DataYAG_IntNormModel: Boltzmann Chi^2 = 0.00006R^2 = 0.99663 A1 1 ±0ns

ity

100000

150000

nten

sity

[cou

n 400.0 K 425.0 K 450.0 K 475.0 K 500.0 K

0 3

0,4

0,5

0,6 A2 0 ±0x0 528.90146 ±2.20442dx 59.70609 ±1.7384

rmal

ised

Inte

n

0

50000

In

0 0

0,1

0,2

0,3

nor

Ex= 450 nm IntNorm

Thermal quenching of YAG:Ce(2%)

450 500 550 600 650 700 750 8000

Wavelength [nm]250 300 350 400 450 500

0,0

Temperature [K]

Thermal quenching of YAG:Ce(2%)exc = 450 nmem = 560 nm


TQ1/2 = 260 °C

Fundamental Aspects 4fn4fn-15d1 TransitionsA closer look into the thermal quenching of YAG:Ce

70 Reabsorption Tunneling


a) At low Ce3+ concentration < 1% 60

65

70 Reabsorption Tunneling

Quenching due to tunnelingTQ1/2 > 300 °C

45

50

55

ay ti

me

(ns)

b) At high Ce3+ concentration > 1%Quenching due to re-absorption 35

40

45

dec

YAG:Ce 0.033% YAG:Ce 0.333% YAG:Ce 1.0%

TQ1/2 < 300 °C300 350 400 450 500 550 600 650 700

30

temperature (K)

YAG:Ce 3.333%

ConclusionA high activator concentration results in strong re-absorption


and thus in pronounced thermal quenching.

Fundamental Aspects 4fn4fn-15d1 Transitions

4 CB

Example: Eu2+ luminescence in an oxidic host latticeFundamental Aspects 4f 4f 5d Transitions

3 5x104

4,0x104

4,5x104

[Xe]4f65d1 (8HJ)

CBElectron

trapPhotoionisation: E = kT

2,5x104

3,0x104

3,5x10 [ ] ( J)

hEnergy transferh

1 0 104

1,5x104

2,0x104Tunneling probability

~ r = re – rg

0,05,0x103

1,0x104

[Xe]4f7 (8S7/2) Hole trap

Quenching by multiphonon relaxation? Nocross-relaxation? Not li ? Y f l St k Shift S SiO E

VB


tunneling? Yes for a large Stokes Shift: Sr2SiO4:Euphotoionisation? Yes for a small [Xe]4f65d1 to CB distance

Fundamental Aspects 4fn4fn-15d1 Transitions1,0

ty

Example: Eu2+ luminescence in inorganic host lattices


0,6

0,8

d em

issi

on in

tens

it

The Stokes Shift is roughly correlated tothe width of the emission band.

0 0

0,2

0,4

Nor

mal

ised

SrO:Eu is violet-black and not luminescentat ambient temperature due to the very largeSt k Shift 300 400 500 600 700 800

0,0

Wavelength [nm]Stokes Shift.

Phosphor exc [nm] em [nm] Stokes Shift [cm-1] FWHM [cm-1]S B O E 356 367 1030 1420SrB4O7:Eu 356 367 1030 1420 BaMgAl10O17:Eu 408 453 2440 2400BaSi2N2O2:Eu 460 490 1300 1200 1 siteB SiO E 434 505 3240 2360Ba2SiO4:Eu 434 505 3240 2360Sr2SiO4:Eu 440 570 5200 3200MgS:Eu 562 592 900 1120 1 siteCaAlSiN E 530 650 3500 2300


CaAlSiN3:Eu 530 650 3500 2300CaS:Eu 600 654 1330 1460 1 site

Fundamental Aspects 4fn4fn-15d1 TransitionsThermal quenching of AEGa2S4:Eu with AE = Ca, Sr, Ba

15000T25

1 0 Peak intensity


10000

T25 T75 T150 T200 T250T300y

[a.u

.]

0,8

1,0 Peak intensityA1 1,0110A2 0,01594x0 179,41dx 26,696 in

tens

ity

5000

T300 T330

mis

sion

inte

nsity

0,4

0,6 IntegralA1 0,99900A2 0,002116x0 169,99dx 30 894

ativ

e em

issi

on

450 500 550 600 6500

Em

0 50 100 150 200 250 300 3500,0

0,2dx 30,894

y = A2 + (A1-A2)/(1 + exp((x-x0)/dx))

Rel

a

exc = 450 nmem = 525 nmBaGa2S4:Eu Lit.: TQ1/2 = 210 °C

Wavelength [nm] Temperature [°C]

2 4 1/2SrGa2S4:Eu Lit.: TQ1/2 = 200 °CCaGa2S4:Eu Lit.: TQ1/2 = 170 °CQuenching mechanism is photoionisation


Quenching mechanism is photoionisation

Fundamental Aspects 4fn4fn-15d1 Transitions

Sample: BaMgAl O :Eu2+ 0,8

0,9

1,0Sample: BaMgAl10O17:Eu2+

100

K]

Fundamental Aspects 4f 4f 5d TransitionsThermal quenching of AEMgAl10O17:Eu

2,0x106

2,5x106

3,0x106

Ex= 254 nmslit size: Ex = 4.00 nm, Em = 1.00 nm

Sample: BaMgAl10O17:Eu

]

100.0 K 150.0 K 200.0 K 250.0 K 300.0 K350 0 K

0,4

0,5

0,6

0,7

ty [n

orm

alis

ed to

1

1,0x106

1,5x106

Inte

nsity

[cps

] 350.0 K 400.0 K 450.0 K 500.0 K

0,0

0,1

0,2

0,3

Inte

gral

inte

nsit

Integrated IntensityEx= 450 nmTQ= K

300 350 400 450 500 550 6000,0

5,0x105

Wavelength [nm]

100 125 150 175 200 225 250 275 300 325 350 375 400 425 450 475 500

T [K]

1000

Sample: BaMgAl10O17:Eu2+

exc = 254 nmem = 453 nm

1 1 2 5

100

y [c

ount

s]

Ex= 267.0 nm T=100.00 KT=150.00 K1/e = 1.1 µs, 1/10 = 2.5 µs

BAM TQ1/2 = 340 °C SAM TQ1/2 = 300 °C

10Inte

nsity T 150.00 K

T=200.00 K T=250.00 K T=300.00 K T=350.00 K T=400.00 K T=450.00 KT 500 00 K


1/2 CAM TQ1/2 = 80 °C 0 2000 4000 6000 8000 10000

1

time [ns]

T=500.00 K

Fundamental Aspects - Pr3+ LuminescenceFundamental Aspects Pr LuminescencePr3+ ground state configuration[X ]4f2 13 SLJ St t

[Xe]4f2 [Xe]4f15d1

3H[Xe]4f2 13 SLJ-States

4f 5d

603HJ

Pr3+ excited state configuration[Xe]4f15d1

cm-1

] 1S0

50

40

4f 5d

gy[1

03c

30

40

Energy distance between the [Xe]4f2 and [Xe]4f15d1

fi ti i 62000 1

Ene

rg

1D2

3P23P020

3P1, 1I6

configuration is 62000 cm-1

(for free Pr3+ ions)E0(Pr3+/4+) = 3.2 V in [Pr(H2O)9]3+(aq)

3H

2

1G4

3F

103F3

3F4


IE(Pr3+/4+) = 7.8 eV in CaF2(s) 3H4

3H5

3H6F2

0

Fundamental Aspects - Pr3+ LuminescenceTuning the distance between the [Xe]4f2 and [Xe]4f15d1 configuration

Fundamental Aspects Pr Luminescence

Free ion Centroid shift(covalent interaction)

Crystal-fieldsplitting

Stokes Shift

4f15d1

c

3cm

-1]

cfs

ergy

[103

62000 cm-1

[Xe]4f2

Ene

Determining factors: (Spectroscopic) Polarisibility, ion charge density,

[Xe]4f2


Determining factors: (Spectroscopic) Polarisibility, ion charge density, site symmetry, coordination number, metal-ligand distance

Fundamental Aspects - Pr3+ Luminescence

60

[Xe]4f2 [Xe]4f15d1 Oh site distorted Oh site


50

60

3cm

-1] 1S0

40

ergy

[10

30

Ene

1D2

3P23P020

3P1, 1I6

3H3H6

1G4

3F2

103F3

3F4


3H4

3H50

Fundamental Aspects - Pr3+ Luminescence

[Xe]4f15d13HJ,3F2

3P03H6+1D2

3H43P0

3H5

3P03H4

3P 3F3P0

3F2

ex=450nmex=280nmex=160nm

c)b)a) Lu3 ALuAG

Band gap exc. 4f-5d exc. 4f-4f exc.Fundamental Aspects Pr Luminescence

ex=451nm

0% Ga

0 5

308

3P03F4

P0 F2

Lu3 A

l4 G

) Al5 O

12

ex=450nm

20% Ga1

305

GaO

12

nsity

Lu3 A

l3 Ga

ex=449nm

60% Ga

40% Ga

298

301

Rel

ativ

e in

ten

Lu3 A

l2 Ga

3a

2 O12LuAGG

ex=449nm

80% Ga

Lu3 A

lGa

4 O3 O

12

ex=448nm

100% Ga

80% Ga

Lu3 G

a5 O

12

O12

LGG


300 400 500 600 700 800Wavelength (nm)

400 500 600 700 800Wavelength (nm)

500 550 600 650 700 750 800Wavelength (nm)

LGG

Fundamental Aspects - Pr3+ LuminescenceQuenching mechanisms of [Xe]4fn-15d1 to [Xe]4f2 transitions


conduction band

5d 5d

ergy

5d

4fergy

5d

4f

ergy

5d

Ene 4f

Ene En 4f

valence band

0 Q 0 Q0 Q Q

Multi-phonon relaxation(issue for Pr3+)

Thermally activated ionization to conduction band (PI)

Thermally activated intersystem crossing (IC)


(issue for Pr3 )to conduction band (PI)intersystem crossing (IC)

Issues in Phosphor Converted LEDsIssues in Phosphor Converted LEDsRed + Green + Blue

LEDsBlue LED +

yellow phosphorBlue LED +

multiple phosphorsUV LED +

RGB phosphorsLEDs yellow phosphor multiple phosphors RGB phosphors

Inherently most efficient

Fixed white point Fixed white point Fixed white pointefficient

Tunable white point

Bad colour rendering

Good color rendering at high TC

Excellent stability

Very good color rendering

Good stability and

High color rendering

Degradation

Red line emission


g yand reliability

yreliability

Spectral interaction

Red line emission possible

Issues in Phosphor Converted LEDsIssues in Phosphor Converted LEDsNatural garnets: C3A2D3O12 or C3A2(SiO4)3Artificial garnets: Ln3(Al,Ga,Fe,Sc)5O12 C – dodecahedral site (CN = 8)

(C )A – octahedral site (CN = 6)D – tetrahedral site (CN = 4)

Pyrope Mg3Al2Si3O12

Almandine Fe3Al2Si3O12

Spessartite Mn3Al2Si3O12

Unit cell of GrossularCa3Al2(SiO4)3

Andradite Ca3Fe2Si3O12

Grossular Ca3Al2Si3O12


3 2( 4)3Space group Ia-3d (#230) Uvarovite Ca3Cr2Si3O12

Issues in Phosphor Converted LEDs

InGaN LED (Y Gd) Al O :CeInGaN LED (Y Gd) Al O :Ce

First white LED → (Nichia 1996)


50

60

70

ity

Tc = 5270 K CRI = 82Tc = 4490 K CRI = 79T 4110 K CRI 76

InGaN LED (Y,Gd)3Al5O12:Ce

0,8

1,0

[a.u

.]

InGaN LED (Y,Gd)3Al5O12:Ce

30

40

sion

inte

ns

Tc = 4110 K CRI = 76Tc = 3860 K CRI = 73Tc = 3540 K CRI = 70

0,4

0,6

sion

inte

nsity

0

10

20

400 00 600 00 800

Emis

s

400 450 500 550 600 650 700 750 8000,0

0,2Em

iss

Yellowphosphor

Blue LED

Status quo cool white pcLEDs @2012

400 500 600 700 800

Wavelength [nm]400 450 500 550 600 650 700 750 800

Wavelength [nm]

Status quo cool white pcLEDs @2012• CRI ~70 – 80• Color temperature typically 5000 K


Issues in Phosphor Converted LEDs – Ce3+

Nephel- Crystal-field

5d1

Stokes Shift

5.0x104

Issues in Phosphor Converted LEDs Ce

4.0x104 5d1

Nephel-auxeticEffect

Crystal-fieldsplitting

cStokes Shift

[cm

-1]

cfs

3.0x104

00 c

m-1

Ene

rgy

[

2.0x104

ion

~ 50

0

SS

1.0x104

ree

Ce3+

i

0.02F7/22F5/2

4f1

F


Ce3+ [Xe]4f1F5/2

Issues in Phosphor Converted LEDsCe3+ doped Garnets [Xe]4f1 ground state configuration

8.0 eV8.6 eV


Emission spectrum is dominated by two [Xe]4f15d1 – [Xe]4f2 emission bands

[Xe]5d1

6.0 eV

7.0 eV

8.0 eV

CB6.5 eV

V]separated by 2000 cm-1

LiYF4:Ce 300, 315 nmYPO4:Ce 335, 355 nmYBO C 390 415

[Xe]4f1

525

nm46

0 nm

565

nm

5.1 eV

2 4 eVnerg

y[e

V

335

nm

2F7/2YBO3:Ce 390, 415 nmY3Al5O12:Ce 525, 565 nm

Red shift of YAG:Ce PL due to

[ ]2F5/2

VB

2.4 eV

0 eV

En

7/2

Red-shift of YAG:Ce PL due to• Enhancement of c(Ce3+) Quenching due to re-absorption • Replacement of Y3+ by Gd3+ or Tb3+ Quenching due to thermally activated IC• Replacement of Al3+ by Mg2+ and Si4+ Quenching due to thermally activated PI

VB0 eV

• Replacement of O2- by N3- Quenching due to thermally activated PI

Blue-shift of YAG:Ce PL due to • Replacement of Y3+ by Lu3+ Quenching is reduced


• Replacement of Y3 by Lu3 Quenching is reduced • Replacement of Al3+ by Ga3+ or Sc3+ Quenching due to thermally activated PI


Blue LED + yellow Blue LED + green


+ red phosphor + red phosphor

spho

r

osph

or

Dphor

osph

or

D

Red

Pho

Gre

en P

ho

Blu

e L

ED

Red

pho

s

Yello

w p

ho

Blu

e L

ED


400 500 600 700Wavelength [nm]

400 500 600 700Wavelength [nm]

Issues in Phosphor Converted LEDs – Eu2+

2DJ[Xe]4f65d1

Issues in Phosphor Converted LEDs Eu

Crystal fieldsplitting

cStokes Shift

3.0x104

1

cm-1

]

Nephel-auxetic

cfs

2.0x104

4000

cm

-1

Ener

gy[c

effect

on ~

34

SS

E

1.0x104

ee E

u2+

i

0 0 [X ]4f7

Fre

8 8 8 8


0.0 [Xe]4f7 8S7/28S7/2

8S7/28S7/2

Issues in Phosphor Converted LEDsEu2+ Luminescent materials: Colour and colour points


Chemical composition max x yCaS:Eu 655 nm 0.70 0.30CaAlSiN3:Eu 650 nm 0.66 0.34S Si N E 625 0 62 0 38 re

ngth

Nitrides +Sr2Si5N8:Eu 625 nm 0.62 0.38SrS:Eu 610 nm 0.63 0.37Ba2Si5N8:Eu 580 nm 0.52 0.48Sr SiO :Eu 575 nm 0 44 0 50 ta

l-fie

ld s

tr Nitrides +Sulfides

Sr2SiO4:Eu 575 nm 0.44 0.50SrSi2N2O2:Eu 540 nm 0.36 0.61SrGa2S4:Eu 535 nm 0.27 0.69SrAl2O4:Eu 520 nm 0.26 0.55 nd

/or c

ryst

2 4Ba2SiO4:Eu 505 nm 0.16 0.57Sr4Al14O25:Eu 490 nm 0.14 0.35SrSiAl2O3N:Eu 480 nm 0.14 0.30

O 4 0 0 1 0 06 oval

ency

an

Oxynitrides+ Oxides

BaMgAl10O17:Eu 450 nm 0.15 0.06Sr2P2O7:Eu 420 nm 0.17 0.01BaSO4:Eu 374 nm 0.17 0.00SrB O :Eu 368 nm 0 17 0 00 re

ase

of c

oT. Jüstel, University of Applied Sciences Münster, Germany Slide 90

SrB4O7:Eu 368 nm 0.17 0.00

Incr

Issues in Phosphor Converted LEDsStructure and luminescence of (Ca,Sr)S:Eu


• Rock salt structure

Hi h iti it t d O H OS Eu

• High sensitivity towards O2, H2O, diluted acids, etc.

2Ca,Sr

• Activator: Eu2+

– on octahedral AE2+ sites– strong 4f-5d absorption

bands below 550 nm– quantum efficiency > 90% – red emission tunable by y

adjustment of Sr/Ca content


Issues in Phosphor Converted LEDsBody colour and spectra of (Ca1-xSrx)S:Eu


0,8

1,0 SrS:Eu (Sr0.75Ca0.25)S:Eu (Sr0.5Ca0.5)S:Eu (Sr0.25Ca0.75)S:Eu

u.]

S S E C S Estability 0,4

0,6

CaS:Eu

sion

inte

nsity

[a.

SrS:Eu CaS:Eustability

Crystal field strength500 600 700 800

0,0

0,2

Emis

s

Centroid shift500 600 700 800

Wavelength [nm]

Composition QE [%] Abs. [%] LE [lm/W] x yCaS:Eu > 95 > 80 90 0.697 0.303SrS:Eu > 95 > 80 260 0.629 0.370


SrS:Eu 95 80 260 0.629 0.370


Lumen equivalent (LE) of red and broad band emitting


Phosphor Peak at [nm] FWHM [nm] LE [lm/W ]

q ( ) gEu2+ phosphors with a high quantum yield (90 – 100%)

Phosphor Peak at [nm] FWHM [nm] LE [lm/Wopt]

CaS:Eu2+ 654 65 85C AlSiN E 2+ 650 90 125

Co

Lu

CaAlSiN3:Eu2+ 650 90 125SrS:Eu2+ 615 60 200Sr2Si5N8:Eu2+ 615 80 200

olour Rend

minous E

MgS:Eu2+ 591 40 350Ba2Si5N8:Eu2+ 580 60 470

dering

Efficacy


Issues in Phosphor Converted LEDsActivator ions showing red line emission are RE or Mn4+

L W O S


0,8

1,0 Emission spectrum Ex= 404 nm Excitation spectrum Em= 613 nm

x = 0,602y = 0,383

sity

Activator ion max [nm] LE [lm/Wopt]La2W3O12:Sm

0,2

0,4

0,6

norm

alis

ed in

tensEu3+ 590 - 620 220 – 360

Sm3+ 598, 643 240 – 260

250 300 350 400 450 500 550 600 650 700 750 8000,0

Sample: 2006-HB-203/1Wavelength [nm]

Pr3+ 590 - 680 100 – 220

M 4+ 620 680 80 250K2SiF6:Mn (GE Patent)

Mn4+ 620 - 680 80 – 250

0,6

0,8

1,0

60

80

100

Diffuse ref

631 nm

Emission spectrum Excitation spectrum

nten

sity

0,2

0,4

20

40

flectance [%]

Rel

ativ

e in


250 300 350 400 450 500 550 600 650 700 750 8000,0 0

Wavelength [nm]

Issues in Phosphor Converted LEDsPhosphor composition LE [lm/Wopt](Zn,Cd)S:Ag 84

Simplified energy level scheme of Eu3+


( ,Cd)S g 8Zn3(PO4)2:Mn 157Y2O2S:Eu 215Y(V P)O4:Eu 225 3.5x10 4

4.0x10 4 4f72p-1

CT l lY(V,P)O4:Eu 225

(Y,Gd)BO3:Eu 270Y2O3:Eu 285Y W O :Eu 300 ] 5D2 5 10 4

3.0x10 4

5L6

level

Y2W3O12:Eu 300Ba2GdTaO6:Eu 320 BaYB9O16:Eu 340I BO E 360 rg

y [c

m-1

] 5D3

2.0x10 4

2.5x10 4

5D2

5D15D0

LED

InBO3:Eu 360

Monochrome line at LE [lm/Wopt]

Ener

1.0x10 4

1.5x10 40

p585 nm 558 595 nm 475 611 nm 335 0.0

5423

1 0

5.0x10 37F6


700 nm 3

Issues in Phosphor Converted LEDsEu3+ Phosphors: Tungstates and Molybdates – Excitation spectra

(Gd0 5Eu0 5)2WO6

blau emittierende LED(Gd0 5Eu0 5)2WO6

UV emittierende LED1,5 (Gd0.5Eu0.5)2WO6

7F0 nach


0,5

1,0( 0.5 0.5)2 6

0,5

1,0( 0.5 0.5)2 6

0 0

0,5

1,0

1,5 0.5 0.5 2 6

5D1

5D2

5D3

5L65G2

CT 5D4

5L7

0,5

1,0

1,50,0(Gd0.5Eu0.5)2W2O9

ät [a

.u.]

0,5

1,0

1,50,0(Gd0.5Eu0.5)2W2O9

ät [a

.u.]

0 5

1,0

1,50,0

(Gd0.5Eu0.5)2W2O9

5D1

5D2

5D

5G25L7CTät

[a.u

.]

5D

5L6

1,0

1,50,0

(Gd0.5Eu0.5)2W3O12

erte

Inte

nsitä

1,0

1,50,0

(Gd0.5Eu0.5)2W3O12

erte

Inte

nsitä

1,0

1,50,0

0,5

(Gd0.5Eu0.5)2W3O125D2

5L6

5G25CT

D3CT

iert

e In

tens

itä D4

1 0

0,0

0,5

,

no

rmie

LiLa0.5Eu0.5W2O81 0

0,0

0,5

,

no

rmie

LiLa0.5Eu0.5W2O81,50,0

0,5

5L6

5D15D3

25L75D4

no

rmi

5HJ

LiLa0.5Eu0.5W2O8

0,0

0,5

1,0

0,0

0,5

1,0

0,0

0,5

1,0

5HJ

5D1

5D2

5D3

6

5G25L7

CT

5D4


250 300 350 400 450 500 550,

Wellenlänge [nm]250 300 350 400 450 500 550

,

Wellenlänge [nm]

250 300 350 400 450 500 550

Wellenlänge [nm]


(Gd0 5Eu0 5)2WO67F

5D0 nachEu3+ Phosphors: Tungstates and Molybdates – Emission spectra


Building unit: {WO6}-Octahedra

Gd2WO6 3 sites for Ln3+

CN = Gd1 = Gd2 = Gd3 = 80 0

0,5

1,00.5 0.5 2 6

7F47F3

F2

7F1

7F0

CN = Gd1 = Gd2 = Gd3 = 8

Gd2W2O9 2 sites for Ln3+

CN = Gd1 – 8; Gd2 – 90,5

1,0

0,0(Gd0.5Eu0.5)2W2O9

ität [

a.u.

]

Building unit: {WO4}-Tetrahedra1,0

0,0(Gd0.5Eu0.5)2W3O12

mie

rte

Inte

nsi

Gd2W3O12 1 site for Ln3+

CN = 81 0

0,0

0,5

no

rm

LiLa0.5Eu0.5W2O8

LiLaW2O8 1 site for Ln3+

CN = 80,0

0,5

1,0


550 600 650 700,

Wellenlänge [nm]


1 0 100

Emission spectrum

Spectroscopic properties of LiEuMo2O8


0,8

1,0

80

100

Diff

Emission spectrum Excitation spectrum Reflection spectrum

sity

0 4

0,6

40

60

fuse reflecta

mal

ised

inte

n

0,2

0,4

20

40

nce(%)N

orm

200 300 400 500 600 700 8000,0 0

Wavelength [nm]

QE465 = 100% LE = 269 lm/WoptRQ465 = 75% max = 614 nmx = 0.665 centroid= 623 nmy = 0 333 = 0 39 ms


y = 0.333 1/e = 0.39 ms d50 = 4.2 µm

Issues in Phosphor Converted LEDsCsLnSi(CN2)4:Eu (Ln = Y, La, Gd) - tetragonal, space group I4


Trigonal-dodecahedral environment of the rare earth ions in MLn[Si(CN2)4] Ln3Al5O12

4 x O(1)4 x O(2)


Issues in Phosphor Converted LEDsCsLnSi(CN2)4:Eu (tetragonal) Ln = Y, La, Gd


0,5

1,0CT

7F0-5L6

5D0-7F4

5D0-7F2

5D0-7F1CsGdSi(CN2)4: 5% Eu3+

Emission spectraEx= 394 nm

Excitation spectra

1,0 5D0 - 7F4

.] CT

Y3Al5O12:Eu(5%)

0,5

1,00,0CT

7F0-5L6 5D0-

7F4

5D0-7F2

5D0-7F1CsLaSi(CN2)4:Eu3+

Emission spectraEx= 394 nmd

Inte

nsity

0 6

5D0-7F3

Em= 592 nm

0,6

0,85D0 -

7F1

ed in

tens

ity [a

.u

0 5

1,00,0

5D0-7F4

5D0-7F2

5D0-7F1

7F 5L

CT CsYSi(CN2)4:5% Eu Emission spectra

5D0-7F3

Excitation spectraEm= 592 nm

norm

alis

ed

0,2

0,4

5D0 - 7F3

5D0 - 7F2

Nor

mal

ise

250 300 350 400 450 500 550 600 650 700 7500,0

0,5

5D0-7F3

7F0-5L6 Ex= 394 nm

Excitation spectraEm= 592 nm

Wavelength [nm]

250 300 350 400 450 500 550 600 650 700 7500,0

Wavelength [nm]

CT-Level at about 28000 cm-1

LE = 280 - 303 lm/Wopt

Wavelength [nm]


p(J. Glaser, H. Bettentrup, T. Jüstel, H.-J. Meyer, Inorg. Chem. 48 (2010) 2954)

VUV PhosphorsVUV PhosphorsFor Xe excimer lamps

147 172

Resona

Intens

2ndC

on

1stC

ont

150

190 - 700 nm

nce Line

sity [a.u.]

tinuum

tinuum

(quartz) glassWavelength [nm]Phosphor layer

Features of Xe excimer lamps– Discharge efficiency ~ 65%– Hg free

Potential application areas Phosphor layer– Photocopier lamps RGB or B/W– LCD Backlighting RGBHg free

– Fast switching cycles– Temp. independent– Dimmable

High lifetime

LCD Backlighting RGB– Medical skin treatment UV-A/B– Photochemistry UV-A/B/C– Disinfection UV-C– Ultra pure water -


– High lifetime– Solely VUV emission

– Ultra pure water -– Surface/wafer cleaning -

VUV PhosphorsXe Excimer Discharge Lamps – Phosphor Presently applied VUV phosphors

Plasma displays Excimer lamps Spectrum of Osram Planon0 006

VUV Phosphors

Issuesp y p

BaMgAl10O17:Eu BaMgAl10O17:EuY(V,P)O4Zn2SiO4:Mn LaPO4:Ce,Tb 0,004

0,005

0,006x = 0.325y = 0.297Tc = 5920 KLE = 282 lm/WRa14 = 87

ty [a

.u.]

LaPO4:Ce,Tb

BaAl12O19:Mn (Y,Gd)BO3:TbBaMgAl10O17:Eu,Mn(Y,Gd)BO3:Eu (Y,Gd)BO3:Eu 0,002

0,003

Em

issi

on in

tens

it

(Y,Gd)BO3:Eu

BaMgAl10O17:Eu

Y2O3:Eu(Y,Gd)(V,P)O4:Eu

400 500 600 7000,000

0,001

E

Wavelength [nm]

5 – 10 lm/W < 50 lm/W

Problem areasEfficiency Down conversion phosphorsVUV Stability Particle coatings (MgO or Al2O3)Color point Improved red x, y ~ Y2O2S:Eu


p p y 2 2Novel application areas UV phosphors

VUV PhosphorsFor PDPs

VUV Phosphors

BAM:Mn

Zn2SiO4:Mn

(Y,Gd)BO3:Tb

Colour points and decay times

Phosphor x y [ms]B M Al O E 0 148 0 068 1 ( ,Gd) O3: b

LaPO4:CeTbBaMgAl10O17:Eu 0.148 0.068 < 1Y(V,P)O4 0.161 0.133 < 1

Zn SiO :Mn 0 233 0 702 10

Y(V,P)O4:Eu

(Y,Gd)BO3:Eu Y2O3:Eu

Zn2SiO4:Mn 0.233 0.702 10BaMgAl10O17:Mn 0.140 0.695 12(Y,Gd)BO3:Tb 0.324 0.615 8LaPO4:Ce,Tb 0.350 0.582 3

Y(V,P)O4

( , ) 4a O4 Ce, b 0 350 0 58 3

(Y,Gd)BO3:Eu 0.636 0.357 8Y2O3:Eu 0.640 0.346 2.5

BAM:EuY(Y,P)O4:Eu 0.657 0.330 1


VUV PhosphorsFor PDPs

VUV Phosphors

Presently applied shortcoming

B M Al O E t bilit

Novel materials based on hostlattices with suitable band edge

BaMgAl10O17:Eu stability

Zn2SiO4:Mn decay time

BaMg3Al14O25:EuSr6BP5O20:EuBaAl2Si2O8:EuCaAl O E

(Y,Gd)BO3:Eu color pointCaAl2O4:EuLaPO4:Tm

BaAl12O19:Mn

BaAl12O19:MnBaMg3Al14O25:Mn

(Y,Gd)2SiO5:Eu

400 500 600 700

Wavelength [nm]

( , )2 5


g [ ]

VUV PhosphorsVUV Phosphors

VUV phosphors for white Xe2* discharge lampsBaMgAl10O17:Eu 80 lm/Wopt.

Spectrum of Osram Planon

0,005

0,006x = 0.325y = 0.297Tc = 5920 K

LaPO4:Ce,Tb

LaPO4:Ce,Tb 500 lm/Wopt.(Y,Gd)BO3:Tb 530 lm/Wopt.

0,003

0,004

LE = 282 lm/WRa14 = 87

n in

tens

ity [a

.u.]

(Y,Gd)BO3:EuBaMgAl10O17:Eu

(Y,Gd)BO3:Eu 275 lm/Wopt.(Y,Gd)2O3:Eu 290 lm/Wopt.

0 000

0,001

0,002

Em

issi

on

Efficacy < 50 lm/Wel.

Challenges related to VUV phosphors for Xe2* discharge lamps) L ffi D i h h

400 500 600 7000,000

Wavelength [nm]

a) Lamp efficacy Down conversion phosphorsb) VUV Stability Particle coatings (MgO or Al2O3)c) Color point stability Optimized blue phosphord) Novel application areas UV phosphors


d) Novel application areas UV phosphors

Future of Rare Earth PhosphorsApplication in UV emitting fluorescent Xe2* excimer lamps→ Requires development and optimization 1,0 Germicidal Action Curve

Future of Rare Earth Phosphors

→ Requires development and optimization

of phosphors with strong UV emission upon 172 nm

excitation 0,6

0,8

1,0

y (a

.u.)

Germicidal Action Curve

Lamp spectrum of YAlO3:Pr

→ e.g. Ce3+, Pr3+ , Nd3+ activated phosphates

YPO4:Nd 190 nm

L PO P 225 0 0

0,2

0,4

Inte

nsity

LaPO4:Pr 225 nm

YPO4:Pr 233 nm

YAlO3:Pr 245 nm

200 250 300 3500,0

Wavelength [nm]

YAlO3:Pr 245 nm

LuBO3:Pr 257 nm

YBO3:Pr 261 nm

Y2SiO5:Pr 270 nm

Lu3Al5O12:Pr 310 nm

L PO C 320


LaPO4:Ce 320 nm

Future of Rare Earth PhosphorsFuture of Rare Earth Phosphors Application in phosphor converted LEDs with NIR emission→ Broad band NIR emission for sensors and spectroscopyp py

Near UV excitable phosphors for laser displaysNear UV excitable phosphors for laser displays→ excitation at 407 nm (blue-ray laser diode)

As a marker in• biolabels

d t t ti 0 8

1,0

YPO4-Tb YPO4-Dy YPO4-Tm

• product protection• medical imaging

0 4

0,6

0,8

nten

sitä

t

Rare earth ions enable phosphorswith all kind of optical spectra

0 0

0,2

0,4In


p pin the visible, UV and NIR range 300 350 400 450 500 550 600 650 700

0,0

Wellenlänge [nm]

AcknowledgementAcknowledgement

Thanks for your kind attention!

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Rare Earth-The Vitamins of Phosphors(Juestel PGS 2012)€¦ · To My PersonTo My Person Thomas...

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