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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

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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

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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)

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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

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Excitation spectrum of the Er green emission

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IFfast relaxation

thenonly the lowest

level emits

transition is spin forbidden

henceSLOW

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

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

9FAST emissions under (LS, J = 8) excitation

NOTE SLOWemission

at 170 nm!!

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

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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)

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MODELConfiguration 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

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MODEL

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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)

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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

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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, Germany

Prof. G. Zimmerer and Dr G. Stryganyuk

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VISIT the poster of

S. Janus

Mo – P – 087

High energy 4f11 and 4f105d

energy levels of Er3+ in BaF2

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170 nm:slow d (HS)

234.9 nm: fast d (LS) and slow 4f11 2G7/2

263 nm: slow 4f11 2G7/2

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Stokes shift1800 cm-1

SLOW emission from (HS, J = 8)

20FAST emission from (LS, J = 8)

21Energy transfer from the (LS, J = 7) level to 2G7/2

slow 4f11 emissionfrom 2G7/2

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0 20 40 60 80 100 120 140 160 180

y = A1*exp(-x/t1) + y0

t1 = 45.8 ns

co

un

ts

time, ns

BaLaF2:(0.2%)Er

Exc. 157,4nmEmi. 162,5nmTemp. 10K

Fast LS d-emission