1. UV i VUV spectroscopy of BaF 2 :Ce crystals (Report from Hasylab experiments) Andrzej J. Wojtowicz IF UMK Optoelectronics Seminar, Oct. 26, 2009

2. Hasylab experiments, July 2009 and Aug. 2007 Experimental teams: 2009: 2007: Piotr Palczewski, Sebastian Janus Marek Różański, Kinga Jastak Marcin WitkowskiRobert TheisAndrzej Wojtowicz

3. 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

4. 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

5. 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

6. 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)

7. 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

8. 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

9. 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

10. Two kinds of electron states in solid state: 1.Delocalized band states; k-vector 2.Localized (trapped or self-trapped) states; configuration coordinate Q

11. k, wave vector E, electron energy E = E 0 – 2Acoskb Electron band states, linear model of the crystal A – electron transfer rate constant

12. Localized states (carrier trapped at impurity/defect or self-trapped) Additional (linear) term in energy, E lin = -kQ

13. 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

14. 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

15. 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

16. 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

17. ### 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

18. ### 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

19. Crystal field: octahedralcubictetrahedral

20. ### 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

21. ### 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

22. ### 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

23. RT, 137.5, 112, 129 nm

24. 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.

25. ### 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

26. ### 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

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

28. 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

29. 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

30. 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

31. 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

32. ### 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

33. ### 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

34. ### 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

35. ### 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

36. 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

37. 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

38. PBFCeNa12.dat, emi. 321.1 exc. 200 nm 10K

39. 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

40. PBFCeNa16.dat, emi. 321.1 exc. 76.4 nm green 10K

41. ### 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

42. 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)

43. 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)

44. 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)

45. 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)

46. 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

47. 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

48. 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

49. 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