TL of BAM - fh-muenster

Jüstel, Meijerink, Lade, Mayr, Wiechert

Thermoluminescence and Defect Structure of Eu2+ and Mn2+ doped BaMgAl10O17

T. Jüstel1, A. Meijerink2, H. Lade1, W. Mayr1, D. U. Wiechert1

1Philips Research Laboratories Aachen, Germany2Universiteit Utrecht, The Netherlands

e-mail to: [email protected]


Outline• Application areas of BAM

• Crystal structure and luminescence spectra of BAM

• Problem setting

• Thermoluminescence analysis– BAM:Eu– BAM:Mn

• Interpretation and conclusions


Application Areas of BaMgAl10O17:Eu(Mn)

High photoluminescence efficiency and perfect color point for tricolor lamps and emissive displays

Fluorescent Lamps Plasma Displays


Structure of BaMgAl10O17 (BAM)

Eu2+ occupies Ba2+ sites in the conduction layersMn2+ occupies Mg2+ sites in the spinel blocks

Ba2+ coordination sphereLayer structure


Luminescence Spectra of BAM:Eu and BAM:Mn

Excitation bands: 170 nm (host lattice)230 nm (4f5d Eu2+)320 nm (4f5d Eu2+)

Emission band: 453 nm (5d4f Eu2+)515 nm (5d5d Mn2+)

150 200 250 300 3500,0

0,2

0,4

0,6

0,8

1,0

0

20

40

60

80

100

4f5d (Eu2+)Band gap (host lattice)

Reflection [%

] Quantum

efficiency [%]

LO =

QE

*(1-

R)

Wavelength [nm]

Excitation and reflection spectra Emission spectra

350 400 450 500 550 6000,0

0,2

0,4

0,6

0,8

1,0

Eu2+

BAM:10%Eu,1%Mn BAM:5%Mn BAM:10%Eu

Mn2+

Em

issi

on in

tens

ity [a

.u.]

Wavelength [nm]


Problem Setting

Strong degradation during device operation related to– Eu3+ formation– Powder quality (crystallinity) and Ba/Mg/Eu/Al ratio

Change of spectral light output Time dependence of light output

150 200 250 300 3500,0

0,2

0,4

0,6

0,8

1,0

0 h panel operation

phosphor powder

10000 h panel operation

Ligh

t out

put =

QE

*(1-

R)

Wavelength [nm]0 200 400 600 800 1000 1200 1400

0,0

0,2

0,4

0,6

0,8

1,0

BAM U716 improved stoichiometry

Inte

nsity

( a.

u. )

Operation time ( h )


first order (monomolecular) TL kineticsThermoluminescence Analysis

0

2 10 -6

4 10 -6

6 10 -6

8 10 -6

1 10 -5

100 150 200 250 300

TL in

tens

ity

Temperature [K]

E/k = 1500 K

4000

s/ =β

6000

8000

10000

E/k = 2000 K

ITL = NT0s exp -E/kT ⋅ exp - s/β exp -E/kT dTT0

T

s

NT0

b

Randall,Wilkins 1945

: decay frequency

: number oftrapped electrons

: heating rateE : energy trap depth

below excited state


Thermoluminescence Analysis

ITL = NT0s exp -E/kT ⋅ exp - s/β exp -E/kT dTT0

T

first order (monomolecular) TL kinetics

dITLdT

= 0 at T = Tm

β⋅ Ek Tm

2 = s ⋅ exp -E/k Tm

5

10

15

20

25

0 0,002 0,004 0,006 0,008 0,01

ln(T

m2 /b

)

1/Tm

E/k

ln (E/sk)


rel.

light

out

put

Thermoluminescence Analysis of BAM:Eu

Annealing in air at 500°C

temperature [°C]

TL intensity decreasesPeak structure does not changeHigh temperature band shows up

150 200 250 300 350

BAM V1370 initialBAM V1370 0.5h 500CBAM V1370 2.5h 500C

Wavelength [nm]

0

2000

4000

6000

8000

10000

12000

15 K/min28 K/min45 K/min52 K/min

0

1000

2000

3000

4000

5000

6000

-150 -100 -50 0

54K/min44 K/min37 K/min28 K/min22 K/min

-150 -100 -50 0

54 K/min44 K/min37 K/min28 K/min22 K/min

0

500

1000

1500

2000

Temperature [°C]

TL in

tens

ity[c

ps]


0

2000

4000

6000

8000

-150 -100 -50 0

Initial 19-5-000.5h 500C air 30-5-002.5h 500C air 15-6-000.5h 500C N2 25-9-00

TL e

mis

sion

[cps

]

Temperature [°C]

Thermoluminescence Analysis of BAM:EuAnnealing in air or Nitrogen

Annealing in air• Density of shallowtraps decreases

• Density of deep trap(0.3 eV) increases

Annealing in Nitrogen• Deep trap does not show up


Thermoluminescence Analysis of BAM:EuAnnealing in N2 or N2/H2

Annealing in Nitrogen• Density of shallow traps decreases

Annealing in N2/H2• Density of shallow trapsdecreases again• Deep trap does not showup0

2000

4000

6000

8000

-150 -100 -50 0

initial+30´500C N2+2h 500C N2+2h 700C N2+2h 700C N2/H2

Temperature [°C]

6´ ramp=> 37K/min

TL e

mis

sion

[cps

]


Light Output of BAM:EuAnnealing in N2 or N2/H2 at 700°C

Annealing in NitrogenReduces its efficiency over the complete wavelength range

Annealing in N2/H2Restores initial efficiency

0

0,5

1

1,5

2

150 200 250 300 350

BAM initial0.5h 500C N2 2.5h 500C N2 2.5h 500C 2h700°C N2 2.5h 500C 2h700°C N2 2h700°CN2H2

Wavelength [nm]

rel.

light

out

put


10

100

1000

-150 -100 -50 0

exc: 122nmexc 160nmexc 180nmexc 200nmexc 254nmexc 350nm

Temperature [°C]0

0,5

1

1,5

2

150 200 250 300 350

light outputI(TL)/ I (abs)I (TL)/ I (Nas)

Wavelength [nm]

Thermoluminescence Analysis of BAM:EuThermoluminescence vs. Excitation Wavelength

shallow trap structure is independent of excitation energydeep trap glow peak only due to low energy excitation (λ > 180 nm)TL is most intense under band gap excitation

TL e

mis

sion

[cps

]

rel.

light

out

put


0

5000

10000

15000

-150 -100 -50 0

B123 BAM:Mn 5%B124 BAM:Eu 25%WM35 BAM:Eu 1%WM61 BAM:Eu 10%

Temperature [°C]

exc 160 nm38 K/min

Comparison between BAM:Eu and BAM:Mn

Thermoluminescence Analysis of BAM:Mn

BAM:Mn exhibits similar peak structure than BAM:Eu

trap levels are lattice and not activator related

TL e

mis

sion

[cps

]


-10

-5

0

5

10

0 0,002 0,004 0,006 0,008 0,01

BAM:5%Mn


TL-intensity is 2.2 times higher than for BAM:EuTrap depth energy is 0.04 eV smaller than for BAM:Eu

0

5000

10000

15000

20000

-150 -100 -50 0

48 K/min38 K/min28 K/min23 K/min

E/k= 1050 Ks = 2400 min-1

E/k= 800 Ks = 150 min-1

E/k= 600 Ks = 20 min-1

E/k= 550 Ks = 10 min-1

TL e

mis

sion

[cps

]

Temperature [°C]ln

(Tm

2 /b)

1/Tm


BAM:5%Mn - thermal treatment in air


0

1

2

3

150 200 250 300 350

BAM:Mn5% initBAM:Mn5% 2h 500°C

0

5000

10000

15000

20000

-150 -100 -50 0

init2h 500°C air

Light output for λ < 170 nm slightly increasesTL fine structure remain unchanged => trap structure unchangedTL fine structure intensity unchanged => trap density unchanged

Temperature [°C]TL

em

issi

on[c

ps]

Wavelength [nm]

rel.

light

out

put


Interpretation of TL Spectra of BAMAnnealing experiments• In air at 500°C

– reduction of shallow trap density due to diffusion (within the conduction layers)

– Formation of oxygen vacancies due to annealing in N2/H2 during synthesis– oxidation of Eu2+ to Eu3+ (trap at 0.3 eV, color centre), not for Mn2+

• In N2 at 500°C– reduction of oxygen vacancy density due to diffusion– no oxidation of Eu2+

• TL spectrum after annealing in N2/H2 at 500 or 700°C– Increase of oxygen vacancy density due to removal of Oxygen

TL spectra dependent on excitation energy• Photon energy >> band gap: band excitation and efficient ET to Eu2+

• Photon energy ~ band gap: exciton formation and elctron trapping on defects• Photon energy < band gap: 4f5d excitation of Eu2+


Thermoluminescence Model for BAM

Shallow traps are located in the band gap, 0.1 to 0.2 eV below the excited state of Eu2+ and Mn2+

4f5d

Conduction band

4f7( 8S7/2 )

4f65d1

EuEu2+2+ MnMn2+2+0.04 eV

5d5d

Valence band


ConclusionsLight output reduction and deep trap formation (0.3 eV) only occur in presence of Oxygen (only for BAM:Eu)⇒ related to Eu3+ formation

Annealing in reducing atmosphere improves VUV lightoutput and deep traps disappear (reduction of Eu3+ to Eu2+)

⇒ Degradation of BAM:Eu is largely caused by oxidation of the redoxsensitive activator Eu2+

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TL of BAM - fh-muenster