Post on 06-Jan-2016
description
1
FAST AND SLOW VUV/UV EMISSIONS FROM BaF2:Er AND
(Ba,La)F2:Er
Andrzej J. WojtowiczUniwersytet M. Kopernika, Toruń,
Poland
ESTE 2010, WROCŁAW & Piechowice
September 04-09, 2010
2
OUTLINE
Samples and experiments
4f n-15d – 4f nVUV luminescence spectra and time profiles of Er emission in
BaF2:Er, (Ba,La)F2:Erwhat do we get; what did we expect
Excitation spectra; energy levels
MODEL; CONFIGURATION COORDINATE DIAGRAM
BF and BLF sites in BaF2 and BaLaF2
SUMMARYand CONCLUSION
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SAMPLES and EXPERIMENTS
(Ba,La)F2:Er (0.2%) La(20%),
BaF2:Er (0.05%), BaF2:Er (0.075%) crystals
grown at Optovac, MA, USA,
donated by late Prof. A. Lempicki of Boston
University
VUV and UV emission/excitation spectra, and
time profiles measured in 2007, 2008, 2009 and
2010 at Superlumi station of I–beamline, DORIS
III, Hasylab, Hamburg, Germany
Prof. G. Zimmerer (retired), Drs G. Stryganyuk,
A. Kotlov
4
0 50 100 150
y = A1*exp(-x/t1) + y0
t1 = 45.8cou
nts
time, ns
(Ba,La)F2:(0.2%)Er
exc. 157,4nmemi. 162,5nmtemp. 10K
VUV luminescence spectra and time profiles
Similar spectra, very different time profiles
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Er3+; what did we expect?
If relaxation between LS and HS d-levels were slower we could have a fast spin-allowed emissions from
heavy rare earth ions
But why does it work for LaBaF2 and not for BaF2?
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Excitation spectra of Er3+ emissions
Fast emission bands (LS levels, spin-allowed transitions)
Slow emission bands (HS levels, spin-forbidden transitions)
Ground state is LS; 2S+1 = 4, emitting state may be LS or HS, 2S+1 = 6
140 145 150 155 160 165 170
fast (2-42 ns) slow (130-190 ns)
LS 5d(e) 5I7
LS 5d(e) 5I8
2G7/2
2G9/2
in
ten
sity
, ar
b.
u.n
its
wavelength, nm
BaF2:Er (0.075%)10 K, emi 239 nm
2F5/2
HS 5d(e) 5I8
LS 5d(e) 5I8
LS 5d(e) 5I7
fast (2-42 ns) slow (140-180 ns)
(Ba,La)F2:Er (0.2%)10 K, emi 234 nm
150 155 160 165 170
HS 5d(e) 5I8
(Ba,La)F2:Er (0.2%)10 K, emi 170 nm
fast (2-42 ns) slow (140-180 ns)
wavelength, nm
LS 5d(e) 5I8
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Emission and excitation spectra of BaLaF2:Er3+ VUV emissions
150 160 170 180
STOKES SHIFT
1800 cm-1
(Ba,La)F2:Er (0.2%), 10 K, VUV slow emi 170 nm exc 165 nm
inte
nsi
ty,
arb
. u
nit
s
wavelength, nm
140 150 160 170 180 190
(Ba,La)F2:Er (0.2%), 10 K, VUV fast emi 181.2 nm exc 157 nm
inte
nsi
ty,
arb
. u
nit
s
wavelength, nm
STOKES SHIFT
2000 cm-1
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MODEL; CONFIGURATION COORDINATE DIAGRAM
4f n states parabolas intersecting 5d parabolas enable nonradiative energy relaxation process in BaF2 but not
in (Ba,La)F2
NOTE: Er in BLF should
emit from 2G7/2
after excitatio
n into 2nd LS band
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SLOW EMISSION FROM 2G7/2 of Er3+ in (Ba,La)F2
At 10 K excitation into second LS band generates emission from 2G7/2
160 200 240 280 320
fast (2-42 ns), UV/VIS slow (140-180 ns), UV/VIS total (0-190 ns), VUV
inte
ns
ity
, arb
. un
its
wavelength, nm
(Ba,La)F2:Er(0.2%)10 K, exc. 148 nm
2G7/2 151.2 nm
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EXCITATION SPECTRA of BLF and BF sites in BaF2
BF site: 143, 153, 162 nm BLF site: 149, 159, 167 nm
130 140 150 160 170
2F5/2
2G7/2
2G9/2
LS LS
2G7/2
2G9/2
in
ten
sity
, ar
b.
u.n
its
wavelength, nm
BaF2:Er (0.2%)10 K, emi 545 nm
2F5/2
HSBLF sites
LS LS
HS fast (2-42 ns) slow (140-180 ns)
BaF2:Er (0.2%)10 K, emi 163.5 nm
BF sites
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BLF and BF sites in BaF2 and BaLaF2
140 145 150 155 160 165 170
fast (2-42 ns) slow (140-180 ns)
inte
nsi
ty,
arb
. u
nit
s
wavelength, nm
BaF2:Er(0.05%)emi 547 nm, 10 K
(Ba,La)F2:Er(0.2%)emi 170 nm, 10 K
BLF site
BLF site
BLF site
BF site BF site
170 nm: spin-
forbidden from BLF
site, some
overlap
547 nm: parity
forbidden emission from 4S3/2
(Er green emission)BF site: 143, 153, 162 nm BLF site: 149,
159, 165 nm
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Emissions from BLF and BF sites in (Ba,La)F2:Er
160 180 200 220 240 260
exc 149 nm
wavelength, nm
exc 159 nm
fast (2-42 ns)
slow (130-190 ns)
inte
nsi
ty,
arb
. u
nit
s
BLF site
(Ba,La)F2:Er(0.2%)10 Kexc 153 nmBLF
sitefast BLF site
slow
BF siteslow 153 nm excitation tuned to
first LS state of BF site
some excitation delivered to first LS state of BLF site
159 nm excitation tuned to first LS state of BLF site
some excitation via relaxation delivered to HS
state of BLF site149 nm excitation tuned to second LS state of BLF site;
relaxation to 2G7/2
some excitation via relaxation delivered to first LS and HS states of BLF site
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Emissions from BLF sites in BaF2:Er
200 300 400 500 600
4S3/2
emission
d-emission
BLF site
fast (2-42 ns)
slow (130-190 ns)
Time resolved UV - VISemission spectra BaF
2:Er (0.075%)
exc. 159 nm, 10 K
inte
nsi
ty,
arb
. u
nit
s
wavelength, nm
159 nm excitation tuned to first LS state of BLF site
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Emissions from BF sites in BaF2:Er
159 nm excitation tuned to first LS state of BLF site
200 300 400 500 600
4S3/2
emission
fast (2-42 ns)
slow (130-190 ns)
d-emission
BF site
Time resolved UV - VISemission spectra BaF
2:Er (0.075%)
exc. 153 nm, 10 K
inte
nsi
ty,
arb
. u
nit
s
wavelength, nm
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SUMMARY and CONCLUSION
FAST VUV EMISSION observed from Er in BLF sites in BaLaF:Er and BaF2:Er
Only slow, spin-forbidden emission observed fromEr in BF sites in BaLaF2 and BaF2
BLF and BF sites abundant in BaF2
The number of BF sites is reduced in BaLaF2
To optimize material for FAST VUV EMISSIONmore studies of Er emission in mixed crystals are needed
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PhD students
Experiment: S. Janus, P. Palczewski, M. Rozanski, M.
Witkowski
calculations of (Er3+)4f11 energy levels:D. Piatkowski
Prof. M.F. Reid (University of Canterbury,
Christchurch, New Zealand)is gratefully acknowledged for providing
f-shell empirical programs to calculate 4f11 levels
ACKNOWLEDGMENTS