Fast and efficient VUV/UV emissions from (Ba,La)F 2 : Er crystals

1. Fast and efficient VUV/UV emissions from (Ba,La)F2:Er crystals Andrzej J. Wojtowicz,Sebastian Janus and Dawid Piatkowski N. Copernicus University, Torun, Poland ICL ’08 7-11 July 2008, Lyon, France

2. OUTLINE Short Introduction to Rare Earth ions in solid state materials VUV/ UV luminescence and luminescence excitation spectroscopy of (Ba,La)F2:Er;experimental results Model; configuration coordinate diagram Summary

3. INTRODUCTION RE ions: [Xe]4fn, [Xe]4fn-15d Intraconfigurational transitions 4fn→ 4fn (sharp lines, parity forbidden slow emissions) Interconfigurational transitions 4fn→ 4fn-15d broad bands, parity allowed, spin allowed/forbidden, emission fast/slow 5d crystal field states (CF structure), 5d-4fn-1 coupling (imposed on CF structure), f-d exchange splitting (LS and HS states)

4. Er3+; what do we expect? strong Coulomb interaction between 11 4f electrons High energy 4f11 levels (theory: the highest at about 100,000 cm-1, the highest experimentally verified at 63,100 cm-1) 5d levels

5. Excitation spectrum of the Er green emission

6. IF fast relaxation then only the lowest level emits transition is spin forbidden hence SLOW

7. Fast spin-allowed transitions from the (LS, J = 8) level?

8. At 10 K SLOW emission under (LS, J = 7)

9. NOTE SLOW emission at 170 nm!! FAST emissions under (LS, J = 8) excitation

10. SLOW emissions under (LS, J = 7) excitation

11. SUMMARY OF EXPERIMENAL RESULTS EMISSIONS observed at 10 K: FAST d-f emissions under 157 nm excitation (LS, J = 8) SLOW d-f emissions under 165 nm excitation (HS, J = 8) SLOW f-f emissions under 148 nm excitation (LS, J = 7)

12. MODEL Configuration Coordinate Diagram Assumptions: All states of the same electronic configuration have the same equilibrium position BUT The equilibrium positions for states of the 4f11 and 4f105d configurations are different The energies taken from experiment

13. MODEL

14. Summary Relatively slow nonradiative relaxation in (La,Ba)F2:Er between the lowest LS and HS 4f105d levels Fast and efficient 4f105d → 4f11 emissions from the (LS, J = 8) level bypassing (HS, J = 8) 4f105d level 2G7/2 emission under the (LS, J = 7) level excitation at 10 K; indirect identification of the 2G7/2 level 2G7/2 - THE HIGHEST KNOWN EMITTING 4f11-level of Er3+ ion in solid state material (66 100 cm-1)

15. ACKNOWLEDGMENTS S. Janus (PhD student), coauthor: experiment, time profile fits D. Piatkowski (PhD student), coauthor: calculations of (Er3+)4f11 energy levels Prof. M.F. Reid (University of Canterbury, Christchurch, New Zealand)is gratefully acknowledged for providing f-shell empirical programs to calculate 4f11 levels

16. ACKNOWLEDGMENTS SAMPLES and EXPERIMENTS (Ba,La)F2:Er crystals grown at Optovac, MA, USA,donated by Prof. A. Lempicki of Boston University VUV and UV emission/excitation spectra, and time profiles measured in 2007 at Superlumi station of I–beamline, DORIS III, Hasylab, Hamburg, GermanyProf. G. Zimmerer and Dr G. Stryganyuk

17. VISIT the poster of S. Janus Mo – P – 087 High energy 4f11 and 4f105d energy levels of Er3+ in BaF2

18. 170 nm: slow d (HS) 234.9 nm: fast d (LS) and slow 4f112G7/2 263 nm: slow 4f112G7/2

19. Stokes shift1800 cm-1 SLOW emission from (HS, J = 8)

20. FAST emission from (LS, J = 8)

21. slow 4f11 emission from 2G7/2 Energy transfer from the (LS, J = 7) level to 2G7/2

22. Fast LS d-emission