1 Fast and efficient VUV/UV emissions from (Ba,La)F 2 :Er crystals Andrzej J. Wojtowicz, Sebastian Janus and Dawid Piatkowski N. Copernicus University, Torun, Poland ICL ’ 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)F 2 :Er; experimental results Model; configuration coordinate diagram Summary

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

4 Er 3+ ; what do we expect? strong Coulomb interaction between 11 4f electrons High energy 4f 11 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 FAST emissions under (LS, J = 8) excitation NOTE SLOW emission at 170 nm!!

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 4f 11 and 4f 10 5d configurations are different The energies taken from experiment

13 MODEL

14 Summary Relatively slow nonradiative relaxation in (La,Ba)F 2 :Er between the lowest LS and HS 4f 10 5d levels Fast and efficient 4f 10 5d → 4f 11 emissions from the (LS, J = 8) level bypassing (HS, J = 8) 4f 10 5d level 2 G 7/2 emission under the (LS, J = 7) level excitation at 10 K; indirect identification of the 2 G 7/2 level 2 G 7/2 - THE HIGHEST KNOWN EMITTING 4f 11 -level of Er 3+ ion in solid state material ( cm -1 )

15 ACKNOWLEDGMENTS S. Janus (PhD student), coauthor: experiment, time profile fits D. Piatkowski (PhD student), coauthor: calculations of (Er 3+ )4f 11 energy levels Prof. M.F. Reid (University of Canterbury, Christchurch, New Zealand) is gratefully acknowledged for providing f-shell empirical programs to calculate 4f 11 levels

16 ACKNOWLEDGMENTS SAMPLES and EXPERIMENTS (Ba,La)F 2 :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, Germany Prof. G. Zimmerer and Dr G. Stryganyuk

17 VISIT the poster of S. Janus Mo – P – 087 High energy 4f 11 and 4f 10 5d energy levels of Er 3+ in BaF 2

nm: slow d (HS) nm: fast d (LS) and slow 4f 11 2 G 7/2 263 nm: slow 4f 11 2 G 7/2

19 Stokes shift 1800 cm -1 SLOW emission from (HS, J = 8)

20 FAST emission from (LS, J = 8)

21 Energy transfer from the (LS, J = 7) level to 2 G 7/2 slow 4f 11 emission from 2 G 7/2

22 Fast LS d-emission