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Thermally induced 4f – 5d transitions in LuAlO 3 :Ce (LuAP) A.J. Wojtowicz , S. Janus

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. INTRODUCTION

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Thermally induced 4f – 5d transitions in LuAlO 3 :Ce (LuAP) A.J. Wojtowicz , S. Janus

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  1. Thermally induced 4f – 5d transitions in LuAlO3: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. INTRODUCTION LuAP: 8.34 g/cm3, 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 transitionsgenerating scintillation light A.J. Wojtowicz, SCINT 2007, June 2007

  3. SAMPLES 2 pixels 2x2x10 mm, grown in 2004 at Institute of Electronic Materials Technology, Warsaw, Polandby prof. Lukasiewicz et al LuAlO3:0.07%at Ce, LuAlO3:0.15%at Ce Emission and excitation spectra: Superlumi station, I – beamline, Hasylab, Hamburg, Germany (prof. Zimmerer) A.J. Wojtowicz, SCINT 2007, June 2007

  4. LuAlO3:Ce, luminescence spectrum A.J. Wojtowicz, SCINT 2007, June 2007

  5. Luminescence spectra, summary: Two spin – orbit split bands (1600 cm-1) lowest d → 2F5/2 357 nm lowest d → 2F7/2 379 nm Crystal field structure not resolved more or less comparable intensities A.J. Wojtowicz, SCINT 2007, June 2007

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

  7. EXCITATION SPECTRA, summary: • Strong triple2F → T2 bandtwo strong (306, 295 nm), one weak transitions (276 nm)34 000 ± 1800 cm-1 • Weaker double2F → E band(226, 214 nm) 45 500 ± 1200 cm-1 A.J. Wojtowicz, SCINT 2007, June 2007

  8. Stokes shift ~ 4700 cm-1 • DOMINANT CUBIC FIELD (Oh);10Dq ~ 11 500 cm-1weak low symmetry field~ 1500 cm-1 • The intensity ratio of two d–bands2F → T2 / 2F → E12 K ~4.4298 K~ 3.8 A.J. Wojtowicz, SCINT 2007, June 2007

  9. Both T2 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 A.J. Wojtowicz, SCINT 2007, June 2007

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

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

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

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

  14. THEORY - MODEL D.J. Robbins, YAG J. Electrochem. Soc. 1979 Thermally activated transitions from the higher ground state level Different transition moments BAND SHIFTS p1 < p1’ p1 < p2 p2’ < p1’ A.J. Wojtowicz, SCINT 2007, June 2007

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

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

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

  18. ENERGY LEVEL DIAGRAM, 5d levels Sequence of levels must agree with the experiment Γ7, Γ8 doubled-valued representations of Oh A.J. Wojtowicz, SCINT 2007, June 2007

  19. ENERGY LEVEL DIAGRAM, 4f levels Sequence of levels must agree with the experiment Γ6, Γ7, Γ8 doubled-valued representations of Oh A.J. Wojtowicz, SCINT 2007, June 2007

  20. Transition moment matrix elements(line strenghts) between Γ6, Γ7, Γ8 states originating from 2F7/2 and Γ7, Γ8 states from 2F5/2 term of 4f configuration and Γ8, Γ7 states originating from T2 and E terms of 5d electron configuration T. Hoshina, J. Phys. Soc. Jap., 1980 A.J. Wojtowicz, SCINT 2007, June 2007

  21. A.J. Wojtowicz, SCINT 2007, June 2007

  22. The lowest 4f level (absorption), options: 0.24 is the only option where T2 takes larger share (4.17), consistent with the experiment (3.8–4.4). A.J. Wojtowicz, SCINT 2007, June 2007

  23. The sequence of 5d T2 levels (absorption), relevant matrix elements: Only 4f Γ7 ground state and 5d Γ8 below Γ7 are consistent with two strong and one weak transitions generating 4f 2F5/2 → 5d T2 band A.J. Wojtowicz, SCINT 2007, June 2007

  24. The lowest 5d level (emission), options: Γ8a and Γ8b give reasonable values for the ratios of 2F7/2 and 2F5/2 bands – Γ8 below Γ7 A.J. Wojtowicz, SCINT 2007, June 2007

  25. Thermally induced transitions; line strengths between 5dEΓ8 states and two lowest 4f levels: p1/p2 = 0.2 (experiment 0.15±0.02)p’1/p’2 = 5 (experiment 7±5) A.J. Wojtowicz, SCINT 2007, June 2007

  26. SUMMARY • Dominant cubic and low symmetry crystal field components determine the ground and excited states of the Ce3+ ion in LuAP, in order of increasing energy: • 4f 2F5/2: 2F5/2Γ7, 2F5/2Γ8a, 2F5/2Γ8b • 5d 2D: T2Γ8a, T2Γ8b, T2Γ7, EΓ8a, EΓ8b A.J. Wojtowicz, SCINT 2007, June 2007

  27. 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 BaF2, 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 A.J. Wojtowicz, SCINT 2007, June 2007

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