UV i VUV spectroscopy of BaF2:Ce crystals

(Report from Hasylab experiments)

Andrzej J. Wojtowicz

IF UMK

Optoelectronics Seminar, Oct. 26, 2009

Hasylab experiments, July 2009 and Aug. 2007

Experimental teams:

2009: 2007:

Piotr Palczewski, Sebastian Janus

Marek Różański, Kinga Jastak

Marcin Witkowski Robert Theis

Andrzej Wojtowicz Andrzej Wojtowicz

OUTLINE

Experimental set-up

Samples

Some physics: localized and band states of charge

carriers

UV i VUV spectroscopy of BaF2:Ce crystals:

results and discussion

Summary

OUTLINE

Experimental set-up

Samples

Some physics: localized and band states of charge

carriers

UV i VUV spectroscopy of BaF2:Ce crystals:

results and discussion

Summary

Superlumi station, beamline I, Doris III ring, Hasylab,

DESY, Hamburg, Germany

Prof. G. Zimmerer i Dr Aleksei Kotlov

Funding:UE (via Hasylab; large experimental facilities), IF

UMK

Superlumi station, technical details

Excitation:

synchrotron, McPherson monochromator (primary) ,

grating (spherical mirror) 2 m, 1200 gr/mm, Al+MgF2 (50-330 nm), res. 0.32 nm

Luminescence:

Home-made Pouey VUV monochromator, 0.5 m, f/2.8,

res. 1.1 nm, solar blind R6836 Hamamatsu PMT (115-300 nm)

UV-VIS Monochromator, Acton Research 0.3 m Czerny-Turner SpectraPro300i, f/4, Hamamatsu PMT R6358P (200-800 nm). 3 gratings, 1200 gr/mm (2.7 nm/mm, blazed at 300 nm), 300

gr/mm (10.8 nm/mm, blazed at 300 i 500 nm)

OUTLINE

Experimental set-up

Samples

Some physics: localized and band states of charge

carriers

UV i VUV spectroscopy of BaF2:Ce crystals:

results and discussion

Summary

Samples cut from larger boules: BaF2:0.05m%Ce, 0.2m%Na

BaF2:0.015m%Ce

Grown at Optovac, MA, USA donated by Prof. A. Łempicki of Boston

University

Scintillator, phosphor, laser material

Not the best in any category, convenient as a model material: efficient host-ion energy transfer

emission at 290-350 nm, decay time 25-30 ns, complex spectroscopy

OUTLINE

Experimental set-up

Samples

Some physics: localized and band states of charge

carriers

UV i VUV spectroscopy of BaF2:Ce crystals:

results and discussion

Summary

Two kinds of electron states in solid state:

1. Delocalized band states; k-vector

2. Localized (trapped or self-trapped) states; configuration coordinate Q

k, wave vector

E, electron energy

E = E0 – 2Acoskb

Electron band states, linear model of the crystal

A – electron transfer rateconstant

Localized states (carrier trapped at impurity/defect or

self-trapped)

Additional (linear) term in energy, Elin = -kQ

Band states:electronic energy reduced, no lattice

relaxation

Localized states (self-trapped electrons or holes)

lattice relaxationno electronic energy loss

The question for a free charge carrier in any material

is: localize or delocalize?

Two extreme cases: Si and BaF2

Si, broad cb i vb bands;a lot to gain by staying delocalized

ANDnothing to gain upon localization

(no lattice relaxation; covalent bonds)

Band (quantum mechanical) conduction: high mobility, low effective mass

No self – trapping, no lattice relaxation gain upon trapping at impurity/defect

BaF2:Ce, narrow cb i vb bands;little to gain by staying delocalized

ANDlarge lattice relaxation (ionic bonds)

hole/electron self-trapping, Vk centers, F – H complexes

Bandgap energy 10.6 eV (117 nm), band exciton (n = 1) 10eV (124 nm)

Free excitons – band states (relaxation?)

Bound excitons – combined band and localized states

Electron – hole pairs – band states (relaxation?)

Pay attention to 117 i 124 nm

OUTLINE

Experimental set-up

Samples

Some physics: localized and band states of charge

carriers

UV i VUV spectroscopy of BaF2:Ce crystals:

results and discussion

Summary

### D:\Users\Torun\BFCeNa09.dat, started at 22.07.2009, 02:11.### Scan of ARC (0/0 grating) monochromator from 450.00 to 210.00 nm, with 1.00 nm steps. Using 4 channels, counting time 2.00 s.### Primary monochromator: 200.000 nm (6.199 eV). T Sample: 299.80 K, Doris current: 0.00 mA.### ### BF2Ce(0.05)Na(0.2) ### Exc 200 nm### Temp 302 K### 300/300### slits 0.4 mm

RT, 200 nm

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### D:\Users\Torun\BFCeNa02.dat, started at 21.07.2009, 22:54.### Scan of primary monochromator from 310.00 to 50.00 nm, with 0.20 nm steps. Using 6 channels, counting time 2.00 s.### Monochromator Positions: ARC: 322.99 nm (300/300), VUV: -4.87 nm. T Sample: 305.20 K, Doris current: 0.00 mA.### ### BF2Ce(0.05)Na(0.2) ### Emi 323 nm### Temp 306 K### 300/300### slits 0.4 mm

RT, 323 nm

Crystal field:

octahedral cubic tetrahedral

### D:\Users\Torun\BFCeNa03.dat, started at 22.07.2009, 00:09.### Scan of ARC (300/300 grating) monochromator from 450.00 to 270.00 nm, with 1.00 nm steps. Using 6 channels, counting time 2.00 s.### Primary monochromator: 137.495 nm (9.017 eV). T Sample: 302.30 K, Doris current: 0.00 mA.### ### BF2Ce(0.05)Na(0.2) ### Ex 137.5 nm### Temp 302 K### 300/300### slits 0.4 mm

RT, 137.5 nm

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### D:\Users\Torun\BFCeNa05.dat, started at 22.07.2009, 00:43.### Scan of ARC (300/300 grating) monochromator from 450.00 to 200.00 nm, with 1.00 nm steps. Using 6 channels, counting time 2.00 s.### Primary monochromator: 128.999 nm (9.611 eV). T Sample: 301.50 K, Doris current: 0.00 mA.### ### BF2Ce(0.05)Na(0.2) ### Exc 129 nm### Temp 302 K### 300/300### slits 0.4 mm

RT, 129 nm

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fast slow

### D:\Users\Torun\BFCeNa07.dat, started at 22.07.2009, 01:23.### Scan of ARC (0/0 grating) monochromator from 450.00 to 180.00 nm, with 1.00 nm steps. Using 4 channels, counting time 2.00 s.### Primary monochromator: 112.296 nm (11.041 eV). T Sample: 300.60 K, Doris current: 0.00 mA.### ### BF2Ce(0.05)Na(0.2) ### Exc 112,3 nm### Temp 302 K### 300/300### slits 0.4 mm

RT, 112 nm

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RT, 137.5, 112, 129 nm

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D:\Users\Torun\BFCeNa02.dat, started at 22.07.2009, 00:43 emi. 323 nm, black, total.D:\Users\Torun\BFCeNa02.dat, started at 22.07.2009, 00:43 emi. 323 nm, red, slow.w. D:\Users\Torun\BFCeNa10.dat, started at 22.07.2009, 02:48, emi. 400 nm, blue, total

RT

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total, 400 nm total, 323 nm slow, 323 nm

exc.

### D:\Users\Torun\BFCeA01.dat, started at 16.08.2007, 14:40.### Scan of primary monochromator from 315.00 to 50.00 nm, with 1.00 nm steps. Using 4 channels, counting time 2.00 s.### Monochromator Positions: ARC: 319.99 nm (300/300), VUV: -5.91 nm. T Sample: 298.50 K, Doris current: 99.74 mA.### BaF2:Ce (0.015%), black line

### D:\Users\Torun\BFNaCe01.dat, started at 18.08.2007, 13:59.### Scan of primary monochromator from 300.00 to 65.00 nm, with 0.50 nm steps. Using 4 channels, counting time 3.00 s.### Monochromator Positions: ARC: 323.49 nm (1200/300), VUV: -5.92 nm. T Sample: 297.20 K, Doris current: 101.90 mA.### BaF2:Ce(0.05):Na, red line

RT, 320 nm

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wavelength, nm

total, 0.015m Ce total, 0.05m Ce

e-h pairs

### D:\Users\Torun\BFCeA01.dat, started at 16.08.2007, 14:40.### Scan of primary monochromator from 315.00 to 50.00 nm, with 1.00 nm steps. Using 4 channels, counting time 2.00 s.### Monochromator Positions: ARC: 319.99 nm (300/300), VUV: -5.91 nm. T Sample: 298.50 K, Doris current: 99.74 mA.### BaF2:Ce (0.015%), black line

### D:\Users\Torun\BFNaCe01.dat, started at 18.08.2007, 13:59.### Scan of primary monochromator from 300.00 to 65.00 nm, with 0.50 nm steps. Using 4 channels, counting time 3.00 s.### Monochromator Positions: ARC: 323.49 nm (1200/300), VUV: -5.92 nm. T Sample: 297.20 K, Doris current: 101.90 mA.### BaF2:Ce(0.05):Na, red line

RT, 320 nm

e-h pairs

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spectrum, 0.015mpercent, divisor quotient

114.5 nm

D:\Users\Torun\PBFCeNa01.dat, emi. 323 nm, exc. 200 nm

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Data: PBFCeNa01_BModel: ExpDecay1Equation: y = y0 + A1*exp(-(x-x0)/t1)Weighting: y No weighting Chi^2/DoF = 501314.32481R^2 = 0.98718 y0 25.43469 ±35.58415x0 0.40885 ±--A1 26662.9387 ±--t1 32.64458 ±0.25422

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D:\Users\Torun\PBFCeNa01.dat, emi. 323 nm, exc. 200.0 nm, black.D:\Users\Torun\PBFCeNa02.dat, emi. 323 nm, exc. 137.5 nm, red.D:\Users\Torun\PBFCeNa03.dat, emi. 323 nm, exc. 129 nm, blue.

RT

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D:\Users\Torun\PBFCeNa01.dat, emi. 323 nm, exc. 200.0 nm, black.D:\Users\Torun\PBFCeNa02.dat, emi. 323 nm, exc. 137.5 nm, red.D:\Users\Torun\PBFCeNa03.dat, emi. 323 nm, exc. 129 nm, blue.

RT

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D:\Users\Torun\PBFCeNa01.dat, emi. 323 nm, exc. 200.0 nm, black.D:\Users\Torun\PBFCeNa02.dat, emi. 323 nm, exc. 137.5 nm, red.D:\Users\Torun\PBFCeNa03.dat, emi. 323 nm, exc. 129 nm, blue.

RT

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D:\Users\Torun\PBFCeNa07.dat, emi. 400 nm, exc. 129 nm, black.D:\Users\Torun\PBFCeNa03.dat, emi 323 nm, exc. 129 nm, blue.D:\Users\Torun\PBFCeNa05.dat, emi 323 nm, exc. 112 nm, red.

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### D:\Users\Torun\BFCeNa13.dat, started at 24.07.2009, 17:32.### Scan of ARC (300/300 grating) monochromator from 450.00 to 210.00 nm, with 0.50 nm steps. Using 4 channels, counting time 2.00 s.### Primary monochromator: 199.997 nm (6.199 eV). T Sample: 9.78 K, Doris current: 0.00 mA.### ### BF2:Ce (0.05)Na(0.2)### Exc 200 nm### Temp 10 K### 300/300### slits 0.5 mm

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Exc. 200 nm

### D:\Users\Torun\BFCeNa12.dat, started at 24.07.2009, 16:07.### Scan of primary monochromator from 315.00 to 50.00 nm, with 0.20 nm steps. Using 6 channels, counting time 2.00 s.### Monochromator Positions: ARC: 322.99 nm (300/300), VUV: -4.87 nm. T Sample: 9.25 K, Doris current: 0.00 mA.### ### BF2:Ce (0.05)Na(0.2)### Emi 323 nm### Temp 10 K### 300/300### slits 1 mm

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fast slow reflection

125.6 nm

### D:\Users\Torun\BFCeNa15.dat, started at 24.07.2009, 18:36.### Scan of ARC (0/0 grating) monochromator from 450.00 to 210.00 nm, with 0.50 nm steps. Using 4 channels, counting time 2.00 s.### Primary monochromator: 132.000 nm (9.393 eV). T Sample: 9.78 K, Doris current: 0.00 mA.### ### BF2:Ce (0.05)Na(0.2)### Exc 132 nm### Temp 10 K### 300/300### slits 0.5 mm

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Exc. 132 nm

### D:\Users\Torun\BFCeNa17.dat, started at 24.07.2009, 19:31.### Scan of ARC (0/0 grating) monochromator from 450.00 to 240.00 nm, with 0.50 nm steps. Using 4 channels, counting time 2.00 s.### Primary monochromator: 114.000 nm (10.876 eV). T Sample: 10.18 K, Doris current: 0.00 mA.### ### BF2:Ce (0.05)Na(0.2)### Exc 114 nm### Temp 10 K### 300/300### slits 0.5 mm

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Exc. 114 nm

PBFCeNa12.dat, emi. 321.1 exc. 200 nm blackPBFCeNa13.dat, emi. 321.1 exc. 132 nm redPBFCeNa14.dat, emi. 321.1 exc. 114 nm blue

10K

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PBFCeNa12.dat, emi. 321.1 exc. 200 nm blackPBFCeNa13.dat, emi. 321.1 exc. 132 nm redPBFCeNa14.dat, emi. 321.1 exc. 114 nm blue

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PBFCeNa12.dat, emi. 321.1 exc. 200 nm

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25000Data: PBFCeNa12_BModel: ExpDecay1Equation: y = y0 + A1*exp(-(x-x0)/t1)Weighting: y No weighting Chi^2/DoF = 365535.4731R^2 = 0.98691 y0 0 ±0x0 0.58087 ±--A1 23759.93853 ±--t1 26.88571 ±0.16555

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PBFCeNa14.dat, emi. 321.1 exc. 114 nm blackPBFCeNa15.dat, emi. 321.1 exc. 83.2 nm redPBFCeNa16.dat, emi. 321.1 exc. 76.4 nm greenPBFCeNa17.dat, emi. 321.1 exc. 67 nm blue

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PBFCeNa16.dat, emi. 321.1 exc. 76.4 nm green

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Data: PBFCeNa16_BModel: ExpDecay1Equation: y = y0 + A1*exp(-(x-x0)/t1)Weighting: y No weighting Chi^2/DoF = 288488.1963R^2 = 0.29639 y0 1550 ±0x0 0.594 ±0A1 1675.88236 ±112.34022t1 17.70539 ±1.68786

inte

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10K

### D:\Users\Torun\BFCeA09.dat, started at 18.08.2007, 18:42, red line, emi 323.5 nm.### D:\Users\Torun\BFCeA08.dat, started at 18.08.2007, 18:03, black line, exc. 199.0 nm. Exc. 291 nm – 34,400 cm-1Emi. 303 nm – 33,000 cm-1Stokes shift – 1400 cm-1

10K

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emission excitation

0.015m%Ce

Summary

Excitation spectra point to: dominant cubic crystal field, 10Dq about

15,000 cm-1, low symmetry component about 2000-3000

cm-1 Stokes shift about 1400 cm-1

Three host-ion energy transfer channels 1) „bound exciton”2) „band exciton”

3) electron –hole pairsplus

4) Direct excitation (no host involved)

Summary

Excitation spectra point to: dominant cubic crystal field, 10Dq about

15,000 cm-1, low symmetry component about 2000-3000

cm-1 Stokes shift about 1400 cm-1

Three host-ion energy transfer channels 1) „bound exciton”2) „band exciton”

3) electron –hole pairsplus

4) Direct excitation (no host involved)

Summary

Excitation spectra point to: dominant cubic crystal field, 10Dq about

15,000 cm-1, low symmetry component about 2000-3000

cm-1 Stokes shift about 1400 cm-1

Three host-ion energy transfer channels 1) „bound exciton”2) „band exciton”

3) electron –hole pairsplus

4) Direct excitation (no host involved)

Summary

Excitation spectra point to: dominant cubic crystal field, 10Dq about

15,000 cm-1, low symmetry component about 2000-3000

cm-1 Stokes shift about 1400 cm-1

Three host-ion energy transfer channels 1) „bound exciton”2) „band exciton”

3) electron –hole pairsplus

4) Direct excitation (no host involved)

• direct excitation: fast Ce emission, no rise time, no slow components

• „bound exciton” excitation: fast Ce emission, short rise time, no slow

components

• „exciton” excitation: Ce and host emission, some fast component,

dominant slow components

• „e-h pair” excitation: Ce and host emissions, fast and slow components, branching coefficient dependent on Ce

concentration

• direct excitation: fast Ce emission, no rise time, no slow components

• „bound exciton” excitation: fast Ce emission, short rise time, no slow

components

• „exciton” excitation: Ce and host emission, some fast component,

dominant slow components

• „e-h pair” excitation: Ce and host emissions, fast and slow components, branching coefficient dependent on Ce

concentration

• direct excitation: fast Ce emission, no rise time, no slow components

• „bound exciton” excitation: fast Ce emission, short rise time, no slow

components

• „exciton” excitation: Ce and host emission, some fast component,

dominant slow components

• „e-h pair” excitation: Ce and host emissions, fast and slow components, branching coefficient dependent on Ce

concentration

• direct excitation: fast Ce emission, no rise time, no slow components

• „bound exciton” excitation: fast Ce emission, short rise time, no slow

components

• „exciton” excitation: Ce and host emission, some fast component,

dominant slow components

• „e-h pair” excitation: Ce and host emissions, fast and slow components, branching coefficient dependent on Ce

concentration