Temperature and Time Dependent Spectroscopy of …

Temperature and Time DependentTemperature and Time Dependent Spectroscopy of Luminescent Materials

e

Thomas JüstelMü t U i it f A li d S iMünster University of Applied Sciences

[email protected]

T. Jüstel, University of Applied Sciences Münster, Germany Slide 1

University Siegen @ July 02nd, 2013

Luminescent Materials – Simply Everywhere!Luminescent Materials Simply Everywhere!CRTs Plasma DisplaysLEDs

Fluorescent Lamps EL DisplaysTomographs (CT/PET)


Luminescent Materials – Simply Everywhere!Optical brightening Paint, pulp and paper, washing powder

Product anticounter feiting Bills stamps credit cards tickets etc

Luminescent Materials Simply Everywhere!

Product anticounter feiting Bills, stamps, credit cards, tickets, etc.

Advertisement illumination Ne discharge lamps

Emergenc ill mination Emergenc e its and signs r n a sEmergency illumination Emergency exits and signs, runways

Medical imaging and treatment x-ray converter filmsPsoriasis and jaundice treatmentDental ceramics

Astronomy EUV/VUV-Amplifier

Biochemistry Labels for DNA, RNA, proteins

Solar Cells Down-ShifterDown ConverterDown-ConverterUp-Converter

Telecommunication NIR Amplifier

T. Jüstel, University of Applied Sciences Münster, Germany Slide 3Greenhouses UV-A/B to blue/red converter

OutlineOutline1. Motivation

2. Luminescence Mechanisms

3. Quenching Processes

4. Analytical Access y

5. Examples– Ce3+ activated phosphates and garnetsCe activated phosphates and garnets– Eu2+ activated aluminates and nitrides– Pr3+ activated phosphors– Bi3+ activated VUV to UV converter– Bi activated VUV to UV converter

6. Some Conclusions


1. Motivation1. MotivationIncreasing requirements on the performance of the luminescent screen in fluorescent lamps results in higher wall load and layer temperature!in fluorescent lamps results in higher wall load and layer temperature!

Miniaturisation of fluorescent lamps• Lamp temperature depends on lamp diameter

• TL 36 mm 40 °C• TL 13 mm 60 °C• PL types 70 – 80 °C• CFL 90 – 110 °CCFL 90 110 C• CFL “GLS look-a-like” 100 – 160 °C• QL 200 – 250 °C

• Quantum efficiency decreases with increasing temperature• Excitation and emission spectra broadens with• Excitation and emission spectra broadens with

increasing temperature

Higher resolution and image quality of emissive displaysHigher resolution and image quality of emissive displays

Development goals concerning luminescent materials• Reduce thermal quenching, colour point shift, decay time


q g p y• Improve linearity, efficiency, chemical and photostability

1. Motivation1. MotivationTremendous advances in LED technology

Luminescent screen

1970(G A )P

2013(Al I G )P (I G )N (Al G )N(Ga,As)P

< 0.1 W< 1.0 lm

< 10 lm/W

(Al,In,Ga)P, (In,Ga)N, (Al,Ga)N0.6 - 5 W> 100 lm

up to 273 lm/W!!!< 10 lm/W< 120 °C

< 100 W/cm2

> 120 K/W

up to 273 lm/W!!!120 – 200 °C

100 – 200 W/cm2

2 12 K/W


> 120 K/WYellow, red, IR

2 – 12 K/WUV-A/B/C, all colors, NIR

2. Luminescence Mechanisms2. Luminescence MechanismsAn (inorganic) luminescent material (phosphor) is a material which converts absorbed energy into electromagnetic radiation beyond thermal equilibrium

Host MatrixNumber of sites, coordination number andsymmetry for cations suitable to host activatorOptical band gapPhonon spectrum Eu2+

Dopants, Impurities and Defects ConcentrationForm solid solution change of Tm

Eu2+

Eu2+

Mn2+

Vg m

Particle‘s surfaceSurface potential and morphologyCoatings Light in and outcoupling

VO

Coatings Light in- and outcoupling

Impact on Spectrum, Stability, Efficiency, Linearity,


p , y, y, y,Thermal Quenching, and Decay time

2. Luminescence Mechanisms2. Luminescence MechanismsExcitation by UV or visible radiation

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

activator excitation sensitizer excitationact ato e c tat o se s t e e c tat o

A*

CBS* ETA**

CB

k

A* A*Transfer

kh

Escape Escape

hknr

AVB

SVB

A

kr

IQE = Act = kr/(kr + knr) = /0 EQE = Act * Transfer* Escape


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

2. Luminescence MechanismsExcitation by VUV or EUV radiation


CB

Excitation energy > or ~ EG of the host lattice Band-to-band excitation

CBA*

PI

Eg

Electrontrap

transfer

A*

Eg

transfer

A*Electron

trapEscapeEscape

h

A+

Eg

AA+

Eg

AHoletrap

Holetrap

hh

EQE = * * * (1 )

VB VBtraptrap

EQE = Act* Transfer * Escape * (1- PI)

Probability of photoionisation (PI) depends on energy distance


y p ( ) p gyof the excited state to the conduction band edge


Ch i Sti l t d l i

2. Luminescence MechanismsPhoto or Thermal Stimulated Luminescence (PSL or TSL)

Charging Stimulated luminescenceCBCB

Electron trap

Stimulation Tunneling

x-rays

or UV

trap

Hole trap

h

VB

Stimulation by photons: Photostimulated Luminescence (PSL) “Storage phosphors”


Stimulation by thermal energy: Thermostimulated Luminescence (TSL) “Afterglow phos.”

2. Luminescence Mechanisms - RE Ions2. Luminescence Mechanisms RE IonsThe Dieke diagram displays all energy levels of the free“CT

CT

5d

5d

5d

5d

5d

5d energy levels of the „free Ln3+ ions: [Xe]4fn configuration5d

5d

5d

5d

Incorporation into a host crystal-field splitting, whichchanges the position by only

5d

5d changes the position by onlya few 100 cm-1

interaction with low-lyingy gCT levels (Eu3+, Yb3+) splitting of the degeneratedl l f th [X ]4fn 15d1level of the [Xe]4fn-15d1

configuration into 2 to 5CF components (Ce3+, Pr3+, ….)


CF components (Ce , Pr , ….)

2. Luminescence Mechanisms - Ce3+ vs. Eu2+2. Luminescence Mechanisms Ce vs. EuCe3+ Eu2+[Xe]4f1 [Xe]5d1 [Xe]4f7 [Xe]4f65d1

60 60

cm-1

]

50

40

2DJ

cm-1

]

50

40

rgy

[103

30

40

gy[1

03

30

40

6

6I7/2

6D9/2 8HJ

Ene

r

20 Ene

rg

20

6P7/2

2F

10 10


2F5/2

2F7/20 0 8S7/2

2. Luminescence Mechanisms - Eu2+

crystal field

8H7/2[Xe]4f65d1

2. Luminescence Mechanisms Eu

crystal fieldsplitting

εcentroid Stokes Shift3.0x104

00 c

m-1

6P7/2

cm-1

]

centroidshift

εcfs

2.0x104

se ~

340

0

Ener

gy[c

gas

phas

SS

E

1.0x104

+in

the

g

0 0 [X ]4f7

Eu2+

8 8 8 8


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

8S7/28S7/2

2. Luminescence Mechanisms - Eu2+

Example: Eu2+ luminescence in borates and fluorides1,0

KMgF3:Eu2+(1,0%)

2. Luminescence Mechanisms Eu

0,6

0,8

,

a.u.

]

Early example: SrB4O7:Eu2+

4f-4f emission at 4 K4f 5d i i t 293 K

0,2

0,4

Inte

nsity

[a

Em Ex= 254 nm

4f-5d emission at 293 K 6P7/2 is just below lowestCF-component of [Xe]4f65d1, while the latter is thermally

250 300 350 400 450 5000,0

Wavelength [nm]

Ex Em= 358 nm

1,0NaMgF3:Eu2+(1,0%)

Em = 254 nm

ypopulated at room temperature

G. Blasse, B.C. Grabmeier“L i t M t i l ”

0,6

0,8

t [a.

u.]

Em Ex= 254 nm Ex Em= 360 nm

“Luminescent Materials”Springer-Verlag 1994

KMgF3:Eu2+ 6P7/2 8S7/2

0,2

0,4

Inte

nsitä

tg 3 7/2 7/2

CFS

N M F E 2+ 6P 8S


250 300 350 400 450 5000,0

Wellenlänge [nm]

NaMgF3:Eu2+ 6P7/2 8S7/2+ [Xe]4f65d1 8S7/2

2. Luminescence Mechanisms - Pr3+

Pr3+ ground state configuration[Xe]4f2 13 SLJ States

[Xe]4f2 [Xe]4f15d1

3

2. Luminescence Mechanisms Pr

[Xe]4f2 13 SLJ-States

4f 5d

603HJ

Pr3+ excited state configuration[Xe]4f15d1 2 SLJ-States cm

-1] 1S0

50

40

E =

4f 5d

rgy

[103

c

30

40

= 62000 c

[Xe]4f2 – [Xe]4f2 transitions Ener

1D2

3P23P020

3P1, 1I6

cm-1

[Xe]4f2 – [Xe]4f15d1 transitions

3H

2

1G4

3F

103F3

3F4


3H4

3H5

3H6F2

0

2. Luminescence Mechanisms - Pr3+2. Luminescence Mechanisms Pr

crystal field3H[Xe]4f15d1

60 crystal fieldsplitting

εcentroid Stokes Shift

00 c

m-1

50

60

centroidshift

εcfse

~ 62

00 1S0

03cm

-1]

40

as p

has

SS

ergy

[10

30

in th

e gEn

20

[X ]4f2

Eu2+

3 3 3 3

10


[Xe]4f2 3H43H4

3H43H4

2. Luminescence Mechanisms - Pr3+

60

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

2. Luminescence Mechanisms Pr

50

60

3cm

-1] 1S0

40

ergy

[10

30

Ene

1D2

3P23P020

3P1, 1I6

3H3H6

1G4

3F2

103F3

3F4


3H4

3H50

3. Quenching Processes3. Quenching Processes1. The absorbed energy does not reach the activator ion (transfer)

a) Competitive absorptionb) 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)) g g p ( g)b) Multi-phonon relaxationc) Cross-relaxationd) Photoionisation

A*

e) Energy transfer to quenching sites = f(T)

3. Emitted radiation is re-absorbed by the luminescent material (esc)) S lf b ti d t t l l

1,0

A

a) Self-absorption due to spectral overlap between excitation and emission bandb) Additional absorption bands due to degradation of the material e g by colour centre formation 0 2

0,4

0,6

0,8

Nor

mal

ized

inte

nsity

(a.u

.)


of the material, e.g. by colour centre formation200 300 400 500 600 700 800

0,0

0,2

Wavelength (nm)

3. Quenching ProcessesRelated to the activator (IQE) and to the host matrix (EQE)


I t l Q t Effi i

CB

Internal Quantum EfficiencyIQE = act

= kr/(kr + knr) = /0

A*

CB /0(Anti proportional to decay time)Decay time (Fluorescence spectrometer)abs

A

Egtransfer External Quantum Efficiency

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

act escape

A

VB

A+

transfer act esc(No correlation to decay time!)Emission spectrum (Ulbricht sphere)

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


( y )Reflection spectrum (Ulbricht sphere)

3. Quenching Processes3. Quenching ProcessesRelated to the activator ions (centre luminescence)

R l t hi h iRelevant quenching mechanismsa) Relaxation to the ground state (direct)• Stokes Shift = Energy distance between

b ti d i i b dabsorption and emission bandS = Sehwe + Sghwg

• FWHM ~ S• Thermal quenching increases with

increasing r = re – rg andr depends on activator-host lattice interactioninteraction Ce3+, Eu2+, Bi3+, Pb2+

b) Relaxation to the ground state via a low lying CT state (indirect)low-lying CT state (indirect) Eu3+, Sm3+

c) Multiphonon and cross-relaxation P 3+ Nd3+ H 3+ E 3+


Pr3+, Nd3+, Ho3+, Er3+

3. Quenching Processes3. Quenching ProcessesRelated to the host matrix (Photoionisation and ET to defects/impurities)

CBElectronPhotoionisation = f(E)

Ln*trap

( )

Energy transfer Results in a reduction of the decay time of Ln*gy

to quenching site

hkrknr

Ln

kr knr

VB

Hole trap

LnVan Schaik et al.,

Electrochemical Society (1994)


VB

3. Quenching ProcessesRelevant mechanisms for the quenching of luminescent materials


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)

Tunneling to the ground stateor thermally activated


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

4. Analytical Access4. Analytical AccessBy a modular spectrometer

DetectorD2-Lamp Detector

Em-Mono

VUV-Mono

Sample chamber


4. Analytical AccessTemperature adjustable sample holder

4. Analytical Access

a) Nitrogen cooled cryostat, MicrostatNfrom Oxford Instruments•Temperature range: 77 - 500 K

• Adjustable sample holders accommodate samples up to

8 mm thickness Temperature range: 77 500 K • Fast cool down: 80 K in less than 10 minutes b) 800 K-Heater•Temperature range: 300 - 800 K

• Suitable for reflection, excitation, and emission p g

• Fast heat up: 800 K in less than 5 minutes experiments


MicrostatN (Oxford Instruments) 800 K-Heater

4. Analytical AccessExcitation sources


a) Thermal quenching and thermoluminescence experiments• Deuterium lamp DS-775 (115 - 370 nm) • 450 W Xe discharge lamp (250 – 1100 nm)

b) Time resolved spectroscopy• µF920H Flash lamp (250 - 1100 nm); pulse width 1.1 µsµF920H Flash lamp (250 1100 nm); pulse width 1.1 µs• EPLED265 ps LED EM = 267.0 nm; pulse width = 800 ps• EPL375 ps LASER EM = 377.6 nm; pulse width = <70 ps

EPL450 ps LASER = 455 6 nm p lse idth = <70 ps• EPL450 ps LASER EM = 455.6 nm; pulse width = <70 ps


4. Analytical Access I

Decay exp. Pulsed, intensive light source• µs flash lamps

4. Analytical Access I

I0Excitation pulse

• µs-flash lamps• ns-flash lamps• Lasers

eNe

t

1/e

logI• LEDs krknr

logII0

1/e

Procedure• Pulse or continuous wave excitation of the sample

gNg

tp• Measurement of the luminescence intensity I at max as function of

time after the excitation source has been switched off • Fitting of the obtained decay curve with one or several e functions• Fitting of the obtained decay curve with one or several e-functions

Imax(t) = A0 + B1*exp(-t/1) + B2*exp(-t/2) + ........


Internal quantum efficiency (IQA): IQA = Act = kr/(kr + knr) = /0

4. Analytical AccessExamples: Mono- and bi-exponential decay


(Y,Gd)2O3:Eu3+(5%) Zn2SiO4:Mn2+(10%)

1. Mono-exponential behavior, e.g. Eu3+, Gd3+, Tb3+

2. Bi-exponential behavior, e.g. Mn2+ ions and Mn2+ - Mn2+ pairs (Y,Gd)2O3:Eu (5%) Zn2SiO4:Mn (10%)

1

m

1000

10000

m

Fit function Fit function 1

0,1

nsity

at 5

30 n

m

100

nsity

at 6

11 n

m

0,01

Inte

n0 2 4 6 8 10

1

10Inte

n

Fit function 2

B1 = 1.0 1 = 1.1 ms B1 = 0.44 1 = 5.6 msB2 = 0.56 2 = 2.3 ms

0 10 20 30 40

t [ms]

0 2 4 6 8 10

t [ms]


B2 0.56 2 2.3 msH. Bechtel, T. Jüstel, H. Nikol, C.R. Ronda, D.U. Wiechert, E. vd Kolk, P. Dorenbos, C.W.E. van Eijk,Optimised Co-activated Willemite Phosphors for Application in Plasma Display Panels, J. Luminescence 87-89 (2000) 1246

4. Analytical AccessThermal quenching experiments Heated/cooled sample holder


Temperatur

400

500

Messphase

ur [K

]

Temperatur

200

300

Tem

pera

tuAufheizphase

Procedure0 20 40 60 80 100 120 140

100

Zeit [min]

• Heating up to temperature T (step wisely)• Measurement of the emission spectrum at max upon excitation of the

sample at excp exc.• Plotting of the integral and/or of the peak intensity as function of T• Fitting of the obtained quenching curve by a Boltzmann-Sigmoidal-function

I(T) = A + I /(1 + Bexp(-E/kT)) Struck-Fonger-Model“


I(T) = A0 + I0/(1 + Bexp(-E/kT)) „Struck-Fonger-Model

4. Analytical AccessExample: SrGa2S4:Eu Integral and peak intensity as function of temp.


10000

15000 T25 T75 T150 T200T250.u

.] 0,8

1,0 Peak intensityA1 1,0110A2 0,01594x0 179,41

tens

ity

5000

10000 T250 T300 T330

sion

inte

nsity

[a.

0,4

0,6 IntegralA1 0,99900A2 0,002116x0 169 99

dx 26,696

ve e

mis

sion

int

0

5000

Em

iss

0,0

0,2

x0 169,99dx 30,894

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

Rel

ativ

exc = 450 nm = 525 nm

450 500 550 600 6500

Wavelength [nm]0 50 100 150 200 250 300 350

0,0

Temperature [°C]

em = 525 nmBaGa2S4:Eu Lit: T1/2 = 210 °C SrGa2S4:Eu Lit: T1/2 = 200 °C Found: T1/2 = 170 °C Strong sample dependenceC G S E Lit T 170 °C


CaGa2S4:Eu Lit.: T1/2 = 170 °C

5. Ce3+ Activated Phosphates and Garnets5. Ce Activated Phosphates and GarnetsLuminescence in YPO4 and Y3Al5O12

Unit Cell of YPO4 Unit Cell of Y3Al5O121. Coordinationsphere of Y3+/Ce3+

4 x O(1) 7.2484 x O(2) 7.193

Low charge density on oxygen

4 x O(1) 7.5284 x O(2) 7.504

High charge density on oxygen


Low charge density on oxygenCe3+ shows UV-A emission

High charge density on oxygenCe3+ shows visible emission

5. Ce3+ Activated Phosphates and GarnetsYPO4:Ce(5%)

5. Ce Activated Phosphates and Garnets

0 8

1,0

Thermal quenching

ity

60000

70000Emission spectra (254 nm excitation)

NP80503025C NP80503075C NP80503150CNP80503200C

nts]

UV-B

UV-A

0,6

0,8

mis

sion

inte

nsi

30000

40000

50000NP80503200C NP80503250C NP80503300C NP80503330C

inte

nsity

[Cou

n

0,2

0,4

integral I354nm

Rel

ativ

e em

10000

20000

30000

Em

issi

on

T1/2 is estimated to be above 700°C!

0 50 100 150 200 250 300 3500,0

Temperature [°C]

300 350 400 450 5000

Wavelength [nm]

1/2

UV-B to UV-A ratio remains constant between RT and 330 °C355 nm band increases at the cost of the 335 nm band with increasing temp.

T Jü t l P H t W M D U Wi h t T t D d t S t f M PO


T. Jüstel, P. Huppertz, W. Mayr, D.U. Wiechert, Temperature Dependent Spectra of MePO4(Me = Ce, Pr, Nd, Bi), J. Luminescence 106 (2004) 225

5. Ce3+ Activated Phosphates and Garnets5. Ce Activated Phosphates and GarnetsY3Al5O12:Ce(1%)

200000

250000Sample: Y3Al5O12:Ce3+

250.0 K 275.0 K 300.0 K

0 8

0,9

1,0TQ50= 530 K (257 °C)

Data: DataYAG_IntNormModel: Boltzmann

150000

200000

[cou

nts]

325.0 K 350.0 K 375.0 K 400.0 K 425.0 K 450 0 K 0,5

0,6

0,7

0,8 Chi^2 = 0.00006R^2 = 0.99663 A1 1 ±0A2 0 ±0x0 528.90146 ±2.20442dx 59.70609 ±1.7384d

Inte

nsity

50000

100000

Inte

nsity

450.0 K 475.0 K 500.0 K

0,2

0,3

0,4

norm

alis

e d

450 500 550 600 650 700 750 8000

Wavelength [nm]250 300 350 400 450 500

0,0

0,1

Temperature [K]

Ex= 450 nm IntNorm

YAG:Ce(2%) exc = 450 nm and em = 560 nm T1/2 = 257 °CThermal quenching due to tunneling increases with Ce3+ conc. and red-shift of


emission band

5. Ce3+ Activated Phosphates and GarnetsA closer look into the thermal quenching of Y Al O :Ce

70 Reabsorption Tunneling

5. Ce Activated Phosphates and Garnets

quenching of Y3Al5O12:Ce

0 = 65 ns 55

60

65

(ns)

a) At low Ce3+ concentration < 1%Quenching due to tunneling

45

50

deca

y tim

e (

Que c g due to tu e gT1/2 >300 °C

b) At high Ce3+ concentration > 1% 30

35

40 YAG:Ce 0.033% YAG:Ce 0.333% YAG:Ce 1.0% YAG:Ce 3.333%

b) At high Ce3+ concentration > 1%Quenching due to re-absorptionT1/2 < 300 °C

300 350 400 450 500 550 600 650 70030

temperature (K)

Conclusion: Ce3+ concentration of garnet should be below 1%, if it is exposed to high excitation density and/or temperature ceramics


C.R. Ronda, A. Meijerink et al., J. Luminescence (2010)

5. Ce3+ Activated Phosphates and Garnets5. Ce Activated Phosphates and Garnets

Sample: Lu3Al5O12:Ce3+ Lu3Al5O12:Ce(0.5%)

0,8

0,9

1,0

TQ50= 803 K (530 °C)Data: DataLuAG_IntNormModel: Boltzmann

300000

350000

p 3 5 12

250.0 K 275.0 K 300.0 K 325.0 K

2F5/22F7/2

0,5

0,6

0,7 Chi^2 = 0.00023R^2 = 0.82907 A1 1 ±0A2 0 ±0x0 803.27079 ±68.2418d 145 53693 26 87841

sed

Inte

nsity

150000

200000

250000

ity [c

ount

s]

350.0 K 375.0 K 400.0 K 425.0 K 450.0 K 475 0 K

0,2

0,3

0,4 dx 145.53693 ±26.87841

norm

alis

45050000

100000

150000

Inte

ns 475.0 K 500.0 K

250 300 350 400 450 5000,0

0,1

Temperature [K]

Ex= 450 nm IntNorm

500 550 600 6500

Wavelength [nm]

LuAG:Ce(0.5%) exc = 450 nm and em = 525 nm T1/2 = 530 °CNo decrease in decay time 0 = 54 nsDecrease of the intensity of the 2D - 2F7/2 transition at the cost of the 2D - 2F5/2


Decrease of the intensity of the D F7/2 transition at the cost of the D F5/2transition is due to an increase of re-absorption (esc)

5. Eu2+ Activated Aluminates and Nitrides

Sample: BaMgAl O :Eu2+ 0,8

0,9

1,0Sample: BaMgAl10O17:Eu2+

100

K]Thermal quenching of AEMgAl10O17:Eu

5. Eu Activated Aluminates and Nitrides

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 nm and em = 453 nm100

y [c

ount

s]

Ex= 267.0 nm T=100.00 KT=150.00 K

1/e = 1.1 µs, 1/10 = 2.5 µsBAM T1/2 = 340 °C SAM T1/2 = 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 T1/2 = 80 °C 0 2000 4000 6000 8000 100001

time [ns]

T=500.00 K

5. Eu2+ Activated Aluminates and NitridesThermal quenching of AEMgAl10O17:Eu


1000

1200Sample: BaMgAl10O17:Eu2+

0,08

0,10Sample: BaMgAl10O17:Eu2+

600

800

me

[ns] 0,06

0,08

100 K

500 K

y

200

400

Ti

average

Boltzmann FitTQ50=

0,02

0,04

B M Al O E (10%) 254 d 453

250 300 350 400 450 5000

Temperature [K]0,10 0,11 0,12 0,13 0,14 0,15 0,16 0,17 0,18 0,19 0,20

0,00

x

BaMgAl10O17:Eu(10%) exc = 254 nm and em = 453 nm0 = 1.1 µsT1/2 = 340 °C


Almost no colour point shift!

5. Eu2+ Activated Aluminates and Nitrides5. Eu Activated Aluminates and NitridesDecay of BaMgAl10O17:EuCo as function of excitation energy

1121 nm140 nm160

Results of a bi-exponential fitI = a1 exp(-t/ t1) + a2 exp(-t/ t2)

Decay curves as function of lambda

0,1

160 nm 170 nm180 nm185 nm190 nm

d in

tens

ity

0,3

0,4

0,08

0,1a1(t = 9 s)a2(t = 100 s)

)

0,01Nor

mal

ised

0,20,04

0,06

a 1(t

= 9

s) a2 (t = 100

Ban

0 0010

0,1

0

0,02

120 140 160 180 200 220

s)

nd edge

0,00110 100

Time (s)

120 140 160 180 200 220Excitation wavelength (nm)

Afterglow occurs under band edge excitation!Excitation at band edge results in hole trapping on Co2+ + h+ Co3+


Excitation at band edge results in hole trapping on Co2+ + h+ Co3+

Delayed reactivation: Co3+ + e- (Co2+)* Co2+ Eu2+

5. Eu2+ Activated Aluminates and NitridesSr4Al14O25:Eu2+(Dy3+)

0 8

1,0 T = 4 Kex = 350 nm Sr4Al14O25:X

1% Eu2+

1% Eu2+, 0.5% Dy3+


Sr4Al14O25:Eu2+

• High efficiency 0 4

0,6

0,8

nten

sity

(a.u

.)

High efficiency• Weak afterglow

0,2

0,4I

Sr4Al14O25:Eu2+Dy3+

• Reduced efficiency• Strong afterglow

250 300 350 400 450 500 550 600 650 7000,0

Wavelength (nm)

106

107

Sr4Al14O25:X

1% Eu2+T = 300 Kex = 350 nm

104

105

10 1% Eu2+, 0.5% Dy3+ 1% Eu

ty (c

ount

s)

101

102

103In

tens

it

T. Jüstel, University of Applied Sciences Münster, Germany Slide 3838-2 0 2 4 6 8 10 12 14

100

Time (min)

5. Eu2+ Activated Aluminates and NitridesSrSi2N2O2:Eu

1,2x107

Emission integral SSL-GM-158-0508-003Ex= 450 nmslit size: Ex = 4.00, Em = 0.60

250 0 K

1000

T=250.00 K T=275.00 KT 300 00 K

Decay Measurement SSL-GM-158-0508-003


T1/2(Integral) = 520 K (247 °C)

6,0x106

8,0x106

1,0x107250.0 K 275.0 K 300.0 K 325.0 K 350.0 K 375.0 K 400.0 Kty

[cou

nts]

100

T=300.00 K T=325.00 K T=350.00 K T=375.00 K T=400.00 K T=425.00 K T=450.00 K

ty [c

ount

s]

T1/2(Decay) = 533 K (260 °C)

0 0

2,0x106

4,0x106

425.0 K 450.0 K 475.0 K 500.0 K

Inte

nsi

10

T=475.00 K T=500.00 K

Inte

nsit

Quenching due tophotoionisation

450 500 550 600 650 700 750 8000,0

Wavelength [nm]

1,0Emission integral SSL-GM-158-0508-003

Model BoltzmannEquation y = A2 + (A1-A2)/(

1 + exp((x-x0)/dx))

0 20 40 60 80 100 120 140 160 180 2001

time [ns]

1200Decay Time SSL-GM-158-0508-003

Model BoltzmannEquation y = A2 + (A1-A2)

/(1 + exp((x x0)/photoionisation

0,6

0,8

Inte

nsity

[a.u

.]

Reduced Chi-Sqr 3,35349E-5

Adj. R-Square 0,99725Value Standard Error

E A1 1 0E A2 0 0E x0 520,38124 1,23589E dx 32,78566 0,98137

600

800

1000

ecay

Tim

e [n

s]

/(1 + exp((x-x0)/dx))

Reduced Chi-Sqr

203,43525

Adj. R-Square 0,9698Value Standard Error

\g(t)\-(average) A1 1185,65373 0\g(t)\-(average) A2 0 0\g(t)\-(average) x0 533,22777 4,57124\g(t)\-(average) dx 27,47347 2,82738

0,2

0,4

Emission IntegralEx= 450 nmTQ50= 520 K (247°C)

Boltzmann Fit

norm

alis

ed

200

400

Emission Intensity Ex= 455.6 nm, Em= 625 nmTQ50 = 533 K (260 °C)

Boltzmann Fit

aver

age

De


250 300 350 400 450 5000,0

Temperature [K]250 300 350 400 450 5000

Temperature [K]

5. Eu2+ Activated Aluminates and Nitrides5. Eu Activated Aluminates and NitridesSrSi2N2O2:Eu4x105

Emission spectraEx= 390 nmslit size: Ex = 4,00, Em = 1.00

100.0 K150.0 K

y

[cou

nts]

2,5x107

3,0x107 Emission IntegralEx= 390 nmslit size: Ex = 5.00, Em = 1.00

100.0 K150 0 Ky

[cou

nts]

Broadening of emission band by increasing t t

2x105

3x105

150.0 K 200.0 K 250.0 K 300.0 K 350.0 K 400.0 K450.0 K

Inte

nsity

1,5x107

2,0x107

150.0 K 200.0 K 250.0 K 300.0 K 350.0 K 400.0 K450.0 K

Inte

nsit

temperature

Weak decrase of emission0

1x105

500.0 K

0,0

5,0x106

1,0x107450.0 K 500.0 K

emission integral by increasing

temperautre

450 500 550 600 650 700 750 8000

Wavelength [nm]450 500 550 600 650 700 750

0,0

Wavelength [nm]0,65

100 K150 K

200 K

Colour Points (C.I.E. 1931)

0 8

1,0TQ Emission Integral

nsity

[a.u

.]

Colour point shifts to red with

increasing0,60

200 K250 K300 K350 K

400 Ky

0,6

0,8

norm

alis

ed In

ten

increasing temperautre

450 K

500 K

0,2

0,4

Emission Integral = 390 nm

n


0,30 0,35 0,400,55

x100 150 200 250 300 350 400 450 500

0,0Ex 390 nm

Temperature [K]

5. Eu2+ Activated Aluminates and Nitrides5. Eu Activated Aluminates and Nitrides

TQ Decay TimeDecay Measurement

SrSi2N2O2:Eu

900

950

TQ Decay Time

ecay

Tim

e [n

s]

1000

Decay Measurement

nsity

[cou

nts] T=100.00 K

T=150.00 K T=200.00 K T=250.00 K T=300.00 KT=350.00 K

850

De

100Inte

n

T=400.00 K T=450.00 K T=500.00 K

750

800

Decay TimeEx= 445.6 nm

10

Rise of afterglow from 100 K to 450 K release of electrons from deep traps

100 150 200 250 300 350 400 450 500

Temperature [K]0 2000 4000 6000 8000 10000

1

time [ns]

p pIncrease of decay time from 100 K to 450 K increase of internal QE due to host lattice expansion

Significantly decrease in decay time from 450 to 500 K


Significantly decrease in decay time from 450 to 500 K thermal quenching sets in at 450 K!

5. Pr3+ Activated PhosphorsYPO4:Pr(1%)

p

1,0

sity

120000

140000 YPO4Pr025C YPO4Pr075C YPO4Pr150CYPO4Pr200C

ts]

0,6

0,8

mis

sion

inte

ns

80000

100000

120000 YPO4Pr200C YPO4Pr250C YPO4Pr300C YPO4Pr330C

nten

sity

[Cou

nt

0,2

0,4

Integral Intensity at 233 nmR

elat

ive

em

20000

40000

60000

Em

issi

on in

0 50 100 150 200 250 300 3500,0

Intensity at 271 nm

Temperature [°C]200 250 300 3500

Wavelength [nm]

Thermal quenching of YPO4:Pr sets in above 300 °C, re-absorption starts @ 75 °C


Thermal quenching of YPO4:Pr sets in above 300 C, re absorption starts @ 75 C

5. Pr3+ Activated PhosphorsY3Al5O12:Pr(1%)

p

15000160 nm Excitation UVC1800025C

UVC1800075C UVC1800150C UVC1800200CUVC1800250Cun

ts]

0,7

0,8

0,9CIE1931 Colour Points

10000UVC1800250C UVC1800300C UVC1800330C

inte

nsity

[Cou

0,4

0,5

0,6

y5000

Em

issi

on

0,1

0,2

0,3330°C

BBL25°C

200 250 300 350 400 450 500 550 600 650 700 750 8000

Wavelength [nm]0,0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8

0,0

x

Y3Al5O12:Pr shows thermal quenching of [Xe]4f15d1-[Xe]4f2 upon feeding [Xe]4f2-[Xe]4f2 luminescence


A. Katelnikovas, H. Bettentrup, D. Dutczak, A. Kareiva and T. Jüstel, On the Correlation between the Composition of B. Pr3+ doped Garnet Type Materials and their Photoluminescence Properties, J. Luminescence 131 (2011) 2754

5. Pr3+ Activated Phosphors(Y,Lu)3(Al,Mg,Si)5O12:Pr3+(1%)

p

1.5

2.0 Lu3Al3MgSiO12:1%Pr3+

nts)

T=100K T=200K T=300K T=400KT=500K

Sample with the weakest crystal-field

t th

1.0

1.5

ity x

105 (c

oun T 500K

Increase of intensityDecrease of

intensity

strength

3.0 T=100KT=200K

Y3AlMg2Si2O12:1%Pr3+

0.5Inte

nsi

2.0

2.5

coun

ts)

T=200K T=300K T=400K T=500K

300 350 400 450 500 550 600 650 700 750 8000.0

Wavelength (nm)

Sample ith the1.0

1.5

tens

ity x

105 (c Considerable decrease

of intensity

Sample with the strongest crystal-field

strength 0.0

0.5

Int


300 350 400 450 500 550 600 650 700 750 800Wavelength (nm)

5. Pr3+ Activated Phosphors

1.0

40 Lu3Al3MgSiO12

p(Y,Lu)3(Al,Mg,Si)5O12:Pr3+(1%)

0.5

nteg

ral i

nten

sity

f-f emission d-f emission

Y AlMg Si O Y Al MgSiO

f-f emission d-f emission

30

35

3P23P

Y3Al3MgSiO12

Y3AlMg2Si2O12

0.0

Nor

mal

ized

in Y3AlMg2Si2O12

200

K

228

K

Y3Al3MgSiO12

20

25

P01D2

y (x

103 c

m-1

)

1.0

gral

inte

nsity

f-f emissiond-f emission

f-f emissiond-f emission 10

153H6

Ene

rgy

0.5

233

K

Lu3AlMg2Si2O12

Nor

mal

ized

inte

g d f emission

277

K

Lu3Al3MgSiO12

d f emission

5

103H4

100 150 200 250 300 350 400 450 5000.0

N

Temperature (K)100 150 200 250 300 350 400 450 500

Temperature (K)

0r'0r0

Energy states of the [Xe]4f2 configuration of Pr3+ are efficiently populated with increased temperature Therefore thermal quenching


populated with increased temperature. Therefore thermal quenching sets in at relatively high temperatures

5. Bi3+ Activated VUV to UV ConverterEfficient phosphors for Xe excimer discharge lamps (172 nm) VUV YPO4:Nd

UV-C YPO4:Bi, CaSO4:Pr,Na

UV B L Al S O Gd L Al S O P UV-B Lu3Al5-xScxO12:Gd, Lu3Al5-xScxO12:PrHighly efficient, pulse driven Xe excimer discharge lamp

Status 2013

• Phosphor efficiency ~ 90%

comprising a UV-C phosphor

• Phosphor efficiency ~ 90%

• Lamp efficiency ~ 30% (YPO4:Bi)

• Instant Trust by PhilipsInstant Trust by Philips

• High wall load desired

Thermal quenching might be an issue!


Thermal quenching might be an issue!

5. Bi3+ Activated VUV to UV ConverterTemperature behaviour of YPO4:Bi

1,0

Thermal QuenchingEmission Spectra

300000Emission Spectra of YPO4:Bi UV-C1303A (160 nm Excitation)

UVC1303A025C

0 6

0,8

on in

tens

ity

200000

UVC1303A075C UVC1303A150C UVC1303A200C UVC1303A250C UVC1303A300CUVC1303A330Cty

[a.u

.]

0,4

0,6

Inte

gral

em

issi

100000

UVC1303A330C

mis

sion

inte

nsit

0 50 100 150 200 250 300 3500,0

0,2

Temperature [°C]

UVC22/03DUVC13/03A

90% at 325°C90% at 230°C

200 250 300 3500

Em

Wavelength [nm] Temperature [ C]

Integral overlap with GACincreases with temperature(emission shifts to 250 nm)

Phosphor shows at 300 °Cless than 10% quenching

Wavelength [nm]


(emission shifts to 250 nm)

6. Some Conclusions6. Some ConclusionsTemperature dependent spectroscopy is a powerful tool to study • Efficiency decrease with temperature i e Final device performance• Efficiency decrease with temperature, i.e. Final device performance

since modern fluorescent light sources operate at elevated temperatureC l i hif i h• Colour point shift with temperature

• Peak broadening and extent of re-absorption

Time dependent spectroscopy is a powerful tool to study • Determine internal quantum efficiency (IQE)• Energy transfer processes to defect sites• Quenching processes due to photoionisation and to diminish them• Quenching processes due to photoionisation and to diminish them

by quenching due to re-absorption


6. Some Conclusions6. Some Conclusions Causes of thermal quenching of a luminescence process

- Tunneling to the ground state = f(Stokes Shift)- Multiphonon relaxation = f(phonon frequency)

Cross relaxation = f(activator distance)- Cross-relaxation = f(activator distance)- ET to defects = f(activator distance)- Photoionisation = f(energy distance to CB)

Measures to reduce thermal quenching- Low activator concentration- Low r = re – rg- Large distance between energy of the excited state and the conduction band edgeg- Low conc. of intrinsic defects and thus high crystallinity- Low conc. of extrinsic defects and thus low impurity level- Energy depletion between ground and excited state level by


Energy depletion between ground and excited state level by centroid shift

AcknowledgementAcknowledgement• Research Group “Tailored Optical Materials“

David Enseling, Florian Baur, David Böhnisch, Tobias Dierkes, DanutaDutczak Stefan Fischer Joana Flottmann Kira Heerdt Benjamin HerdenDutczak, Stefan Fischer, Joana Flottmann, Kira Heerdt, Benjamin Herden, Alexander Hoffmann, Thomas Jansen, Arturas Katelnikovas, Johannes Knossalla, Tim Köcklar, Christian Lenser, Stephan Lippert, Stephanie Möller, Matthias Müller, Dr. Julian Plewa, Patrick Pues, Nele Schumacher, Sebastian Schwung, Ramuas Skaudzias, Claudia Süssemilch, SabaSebastian Schwung, Ramuas Skaudzias, Claudia Süssemilch, Saba Tadesse, Max Volhard, and Nils Wagner

• Universiteit Utrecht, The NetherlandsP f A d i M ij i k f f itf l di iProf. Andries Meijerink for fruitful discussions on luminescence physics

• University of Tübingen Germany• University of Tübingen, GermanyProf. Jürgen Meyer for discussions on crystal structures

• Merck KGaA Darmstadt, Germanyfor generous financial support

T. Jüstel, University of Applied Sciences Münster, Germany Slide 50Thanks for your kind attention…..

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