1. 1 Thermally induced 4f – 5d transitions in LuAlO 3 :Ce (LuAP) A.J. Wojtowicz, S. Janus Institute of Physics, N. Copernicus Univ. Toruń, POLAND IEEE 9th International Conference on Inorganic Scintillators and their Applications, Winston-Salem, NC USA June 4 – 8, 2007

2. A.J. Wojtowicz, SCINT 2007, June 20072 INTRODUCTION LuAP: 8.34 g/cm 3, photofraction 0.3, 365 nm emission, 17 ns decay time, LY over 2xBGO, yet problems GOAL of this work study, report and explain details of optical transitions generating scintillation light

3. A.J. Wojtowicz, SCINT 2007, June 20073 SAMPLES 2 pixels 2x2x10 mm, grown in 2004 at Institute of Electronic Materials Technology, Warsaw, Poland by prof. Lukasiewicz et al LuAlO 3 :0.07%at Ce, LuAlO 3 :0.15%at Ce Emission and excitation spectra: Superlumi station, I – beamline, Hasylab, Hamburg, Germany (prof. Zimmerer)

4. A.J. Wojtowicz, SCINT 2007, June 20074 LuAlO 3 :Ce, luminescence spectrum

5. A.J. Wojtowicz, SCINT 2007, June 20075 Luminescence spectra, summary: Two spin – orbit split bands (1600 cm -1 ) lowest d → 2 F 5/2 357 nm lowest d → 2 F 7/2 379 nm Crystal field structure not resolved more or less comparable intensities

6. A.J. Wojtowicz, SCINT 2007, June 20076 Corrected excitation spectra

7. A.J. Wojtowicz, SCINT 2007, June 20077 EXCITATION SPECTRA, summary:  Strong triple 2 F → T 2 band two strong (306, 295 nm), one weak transitions (276 nm) 34 000 ± 1800 cm -1  Weaker double 2 F → E band (226, 214 nm) 45 500 ± 1200 cm -1

8. A.J. Wojtowicz, SCINT 2007, June 20078  Stokes shift~ 4700 cm -1  DOMINANT CUBIC FIELD (O h ); 10Dq~ 11 500 cm -1 weak low symmetry field ~ 1500 cm -1  The intensity ratio of two d–bands 2 F → T 2 / 2 F → E 12 K ~ 4.4 298 K ~ 3.8

9. A.J. Wojtowicz, SCINT 2007, June 20079  Both T 2 and E d–bands strongly expand toward longer wavelengths with increasing T  Intensities of 5d E subbands; „230 nm” subband increases, „215 nm” subband decreases with T,  „230 nm” subband peak shifts toward lower λ

10. A.J. Wojtowicz, SCINT 2007, June 200710 E subbands positions vs T

11. A.J. Wojtowicz, SCINT 2007, June 200711 Corrected excitation spectra vs T

12. A.J. Wojtowicz, SCINT 2007, June 200712 Corrected excitation spectra vs T

13. A.J. Wojtowicz, SCINT 2007, June 200713 Corrected excitation spectra vs T

14. A.J. Wojtowicz, SCINT 2007, June 200714 THEORY - MODEL D.J. Robbins, YAG J. Electrochem. Soc. 1979 Thermally activated transitions from the higher ground state level Different transition moments BAND SHIFTS p 1 < p 1 ’ p 1 < p 2 p 2 ’ < p 1 ’

15. A.J. Wojtowicz, SCINT 2007, June 200715 5d E subbands intensities vs T

16. A.J. Wojtowicz, SCINT 2007, June 200716 „230 nm” intensity vs T, experiment and theory

17. A.J. Wojtowicz, SCINT 2007, June 200717 „215 nm” intensity vs T, experiment and theory

18. A.J. Wojtowicz, SCINT 2007, June 200718 ENERGY LEVEL DIAGRAM, 5d levels Sequence of levels must agree with the experiment Γ 7, Γ 8 doubled-valued representations of O h

19. A.J. Wojtowicz, SCINT 2007, June 200719 ENERGY LEVEL DIAGRAM, 4f levels Sequence of levels must agree with the experiment Γ 6, Γ 7, Γ 8 doubled-valued representations of O h

20. A.J. Wojtowicz, SCINT 2007, June 200720 Transition moment matrix elements (line strenghts) between Γ 6, Γ 7, Γ 8 states originating from 2 F 7/2 and Γ 7, Γ 8 states from 2 F 5/2 term of 4f configuration and Γ 8, Γ 7 states originating from T 2 and E terms of 5d electron configuration T. Hoshina, J. Phys. Soc. Jap., 1980

21. A.J. Wojtowicz, SCINT 2007, June 200721 5dT 2 Γ 8 a5dT 2 Γ 8 b5dT 2 Γ 7 5dE Γ 8 a5dE Γ 8 b 4f 2 F 7/2 Γ 6 8,571325,71420,0025,714425,714 4f 2 F 7/2 Γ 8 b12,244812,244924,490218,3674 4f 2 F 7/2 Γ 8 a12,244912,24524,4918,3674 4f 2 F 7/2 Γ 7 4,0816 65,3076,1224 4f 2 F 5/2 Γ 8 b6,802833,46962,18761,632641,6327 4f 2 F 5/2 Γ 8 a33,4696,80282,176841,63141,6326 4f 2 F 5/2 Γ 7 34,01434,01381,36058,1632

22. A.J. Wojtowicz, SCINT 2007, June 200722 5d T 2 5d E5dE/5dT 2 4f 2 F 5/2 Γ 8 b42,4600443,26531,02 4f 2 F 5/2 Γ 8 a42,448643,2641,02 4f 2 F 5/2 Γ 7 69,3883316,32640,24 The lowest 4f level (absorption), options: 0.24 is the only option where T 2 takes larger share (4.17), consistent with the experiment (3.8–4.4).

23. A.J. Wojtowicz, SCINT 2007, June 200723 The sequence of 5d T 2 levels (absorption), relevant matrix elements: Only 4f Γ 7 ground state and 5d Γ 8 below Γ 7 are consistent with two strong and one weak transitions generating 4f 2 F 5/2 → 5d T 2 band 5dT 2 Γ 8 a5dT 2 Γ 8 b5dT 2 Γ 7 4f 2 F 5/2 Γ 8 b6,802833,469622,18762 4f 2 F 5/2 Γ 8 a33,4696,80282,1768 4f 2 F 5/2 Γ 7 34,01434,01381,36053

24. A.J. Wojtowicz, SCINT 2007, June 200724 The lowest 5d level (emission), options: Γ 8 a and Γ 8 b give reasonable values for the ratios of 2 F 7/2 and 2 F 5/2 bands – Γ 8 below Γ 7 4f 2 F 7/2 4f 2 F 5/2 TOTAL 5dT 2 Γ 8 a37,142674,2858111,4284 5dT 2 Γ 8 b54,2857474,28622128,57196 5dT 2 Γ 7 114,28725,72495120,01215 5dE Γ 8 a68,571651,4272119,9988 5dE Γ 8 b68,571251,4285119,9997

25. A.J. Wojtowicz, SCINT 2007, June 200725 Thermally induced transitions; line strengths between 5dEΓ 8 states and two lowest 4f levels: 5dE Γ 8 a5dE Γ 8 b 4f 2 F 5/2 Γ 8 b1,632641,6327 4f 2 F 5/2 Γ 8 a41,63141,6326 4f 2 F 5/2 Γ 7 8,1632 p 1 /p 2 = 0.2 (experiment 0.15±0.02) p ’ 1 /p ’ 2 = 5 (experiment 7±5)

26. A.J. Wojtowicz, SCINT 2007, June 200726 SUMMARY  Dominant cubic and low symmetry crystal field components determine the ground and excited states of the Ce 3+ ion in LuAP, in order of increasing energy: 4f 2 F 5/2 : 2 F 5/2 Γ 7, 2 F 5/2 Γ 8 a, 2 F 5/2 Γ 8 b 5d 2 D: T 2 Γ 8 a, T 2 Γ 8 b, T 2 Γ 7, EΓ 8 a, EΓ 8 b

27. A.J. Wojtowicz, SCINT 2007, June 200727  The transition moment matrix elements between these states are consistent with the observed emission and absorption intensities and their temperature dependences  In contrast to Ce–activated YAG and BaF 2, in LuAP, YAP and LuYAP sequence of ground and excited state energy levels may enhance self–absorption of Ce emission;  consequences for scintillation of large crystals; radiation trapping and energy migration