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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

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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

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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