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UV i VUV spectroscopy of BaF 2 :Ce crystals (Report from Hasylab experiments) Andrzej J. Wojtowicz IF UMK Optoelectronics Seminar, Oct. 26, 2009
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Hasylab experiments, July 2009 and Aug. 2007 Experimental teams: 2009: 2007: Piotr Palczewski, Sebastian Janus Marek Różański, Kinga Jastak Marcin WitkowskiRobert TheisAndrzej Wojtowicz
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OUTLINE Experimental set-up Samples Some physics: localized and band states of charge carriers UV i VUV spectroscopy of BaF 2 :Ce crystals: results and discussion Summary
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OUTLINE Experimental set-up Samples Some physics: localized and band states of charge carriers UV i VUV spectroscopy of BaF 2 :Ce crystals: results and discussion Summary
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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
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Superlumi station, technical details Excitation: synchrotron, McPherson monochromator (primary), grating (spherical mirror) 2 m, 1200 gr/mm, Al+MgF 2 (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)
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OUTLINE Experimental set-up Samples Some physics: localized and band states of charge carriers UV i VUV spectroscopy of BaF 2 :Ce crystals: results and discussion Summary
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Samples cut from larger boules: BaF 2 :0.05m%Ce, 0.2m%Na BaF 2 :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
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OUTLINE Experimental set-up Samples Some physics: localized and band states of charge carriers UV i VUV spectroscopy of BaF 2 :Ce crystals: results and discussion Summary
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Two kinds of electron states in solid state: 1.Delocalized band states; k-vector 2.Localized (trapped or self-trapped) states; configuration coordinate Q
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k, wave vector E, electron energy E = E 0 – 2Acoskb Electron band states, linear model of the crystal A – electron transfer rate constant
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Localized states (carrier trapped at impurity/defect or self-trapped) Additional (linear) term in energy, E lin = -kQ
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Band states: electronic energy reduced, no lattice relaxation Localized states (self-trapped electrons or holes) lattice relaxation no electronic energy loss The question for a free charge carrier in any material is: localize or delocalize? Two extreme cases: Si and BaF 2
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Si, broad cb i vb bands; a lot to gain by staying delocalized AND nothing 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
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BaF 2 :Ce, narrow cb i vb bands; little to gain by staying delocalized AND large lattice relaxation (ionic bonds) hole/electron self-trapping, V k 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
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OUTLINE Experimental set-up Samples Some physics: localized and band states of charge carriers UV i VUV spectroscopy of BaF 2 :Ce crystals: results and discussion Summary
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### 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
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Crystal field: octahedralcubictetrahedral
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### 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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### 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 exc.
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### 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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### 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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D:\Users\Torun\PBFCeNa01.dat, emi. 323 nm, exc. 200 nm 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\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. RT
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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 10K Exc. 200 nm
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### 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 10K
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### 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 10K Exc. 132 nm
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### 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 10K Exc. 114 nm
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PBFCeNa12.dat, emi. 321.1 exc. 200 nm black PBFCeNa13.dat, emi. 321.1 exc. 132 nm red PBFCeNa14.dat, emi. 321.1 exc. 114 nm blue 10K
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PBFCeNa12.dat, emi. 321.1 exc. 200 nm black PBFCeNa13.dat, emi. 321.1 exc. 132 nm red PBFCeNa14.dat, emi. 321.1 exc. 114 nm blue 10K
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PBFCeNa12.dat, emi. 321.1 exc. 200 nm 10K
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PBFCeNa14.dat, emi. 321.1 exc. 114 nm black PBFCeNa15.dat, emi. 321.1 exc. 83.2 nm red PBFCeNa16.dat, emi. 321.1 exc. 76.4 nm green PBFCeNa17.dat, emi. 321.1 exc. 67 nm blue 10K
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PBFCeNa16.dat, emi. 321.1 exc. 76.4 nm green 10K
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### 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-1 Emi. 303 nm – 33,000 cm-1 Stokes shift – 1400 cm-1 10K 0.015m%Ce
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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 pairs plus 4) Direct excitation (no host involved)
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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 pairs plus 4) Direct excitation (no host involved)
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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 pairs plus 4) Direct excitation (no host involved)
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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 pairs plus 4) Direct excitation (no host involved)
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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
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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
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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
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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
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