Room temperature fluorescence and excited state dynamics in the near infrared and visible region of U3+ doped LaBr3 single crystals

Article abstract of DOI:10.1016/j.ssc.2005.10.010

Good quality U³⁺ doped LaBr₃ single crystals with a 0.1 mol% U³⁺ nominal concentration have been obtained by the Bridgman-Stockbarger method. Luminescence spectra of the crystals were recorded in a wide spectral range at room temperature. Excitation in the 5f ²6d¹ spectral region produced a strong red and near infrared emission.

Full text of DOI:10.1016/j.ssc.2005.10.010

Solid State Communications 137 (2006) 59–62
www.elsevier.com/locate/ssc
Room temperature fluorescence and excited state dynamics in the near
infrared and visible region of U3C doped LaBr3 single crystals
a
Marcin Sobczyk , Janusz Droz˙dz˙ynski , Radosław Lisiecki , Piotr Solarz ,
a,
b
b
*
´
Witold Ryba-Romanowski b
a Faculty of Chemistry, University of Wrocław, ul. F. Joliot-Curie 14, 50-383 Wrocław, Dolny Slask, Poland
b Institute of Low Temperature and Structure Research, Polish Academy of Sciences, Wrocław, Poland
Received 7 July 2005; received in revised form 11 October 2005; accepted 21 October 2005 by V. Pellegrini
Available online 9 November 2005
Abstract
Good quality U3C doped LaBr3 single crystals with a 0.1 mol% U3C nominal concentration have been obtained by the Bridgman–Stockbarger
method. Luminescence spectra of the crystals were recorded in a wide spectral range at room temperature. Excitation in the 5f26d1 spectral region
produced a strong red and near infrared emission.
q 2006 Elsevier Ltd. All rights reserved.
PACS: 33.50.Dq; 34.50.Gb
Keywords: A. U3C doped crystals; B. Crystal growth; D. Optical properties; D. Nonlinear optics; E. Luminescence
1. Introduction
properties of U3C ions both in room and liquid helium
temperatures have not been performed. In this paper room
temperature luminescence spectra of the U3C ion are for the
first time presented and discussed.
Luminescence properties of numerous lanthanide and
actinide ions doped in various host crystals have been
intensively investigated with respect of their applications in
lasers and nonlinear optics. The actinide ions, as compared
with rare earth ions, exhibit interesting optical properties on
account of the appearance of the first 5fN/5fNK16d1
transitions at lower energies, enabling an easier excitation of
the f-electrons to these broad and intense bands. A number of
single crystals doped with U3C ions have as well been used for
optical amplification in lasers, radars and telecommunication
system [1–4] due to a 2.5 mm emission.
Lanthanum tribromide host crystals are attractive for
spectroscopic investigations of Ln3C and Ac3C ions owing
to their excellent optical properties such as transparency and
low-phonon frequencies. The compound crystallizes in the
hexagonal space group P63/m, with the UCl3 structure and is
isostructural with LaCl3 [5]. The crystal is moderately
hygroscopic and has a maximum phonon energy of about
168 cmK1. Hitherto, exhaustive investigations of the emission
2. Experimental
Single crystals of LaBr3 doped U3C with anominal 0.1 mol%
uranium concentration were grown in silica ampoules using the
Bridgman–Stockbarger method. LaBr3 was synthesized from
La2O3 by the ammonium bromide route and sublimed under
vacuum. UBr3 was prepared according to the procedure reported
in Ref. [6]. The pure host crystals were transparent and colorless,
whereas, the doped crystals were reddish-brown. The dimen-
sions of the crystal amounted to 15!6!4 mm3.
Unpolarized absorption spectra of LaBr3:U3C single
crystals were recorded at 300 K on a Cary 5E NIR-Vis–UV
spectrometer in the 3800–30,000 cmK1 range. Luminescence
spectra were obtained by excitation with an Argon ion laser,
dispersed by a 1-m double grating monochromator with a
spectral bandwidth of 2 cmK1 and were detected by a
photomultiplier with a S-20 or S-1 spectral response. The
resulting signal was analyzed by a Stanford model SRS 250
Boxcar Integrator and stored in a PC computer. Excitation and
luminescence spectra have been obtained by using a Xe LPS-
200Xi lamp and DM 152, DM 711 Dongwoo Optron
*
Corresponding author. Tel.: C48 71 3284901; fax: C48 71 3282348.
´
E-mail address: jd@wchuwr.chem.uni.wroc.pl (J. Droz˙dz˙ynski).
0038-1098/$ - see front matter q 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.ssc.2005.10.010
monochromators with a spectral bandwidth of 0.5 cmK1
.

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M. Sobczyk et al. / Solid State Communications 137 (2006) 59–62
3. Results and discussion
The absorption and excitation spectra of LaBr3:
3C(0.1 mol%) single crystals recorded at room tempera-
U
ture are shown in Fig. 1. In the 4000–19,500 cmK1
absorption range, relatively sharp and well-separated
bands of intraconfigurational 5f3/5f3 transitions have
been observed. In the spectrum recorded at 300 K, the
bands at wavenumbers higher than 19,600 cmK1 are
obscured by strong 5f3/5f26d1 transitions. In comparison
with the low temperature absorption spectrum at 4.2 K one
observes a red shift of the first 5f3/5f26d1 bands of about
1000 cmK1, resulting from strong electron–phonon inter-
actions [7]. In Figs. 2 and 3 the luminescence spectra of
the LaBr3:U3C crystal, obtained by excitation at 488 nm to
the strong 5f26d1 absorption bands are presented. The
excitation energy is then nonradiatively down converted to
4
the D3/2 level. The emission lines observed in the visible
2H(2)11/2
4
region correspond to transitions from the D3/2
,
,
4
4
4F9/2 and G7/2 levels to the I9/2 ground level. The
4
emission from the D3/2 and 2H(2)11/2 levels is not
4
connected with a thermal population of the F9/2 level, in
spite of a small energy gap between these levels (approx.
250 cmK1) because such an emission can be noticed also
at 4.2 K [8]. The weakest emission is observed from the
Fig. 1. Survey room temperature absorption spectrum of the U3C:LaBr3 single
crystal.
G7/2 level. The K15/2/4I11/2 and K15/2/4I9/2 emission
transitions, recorded at temperatures below 80 K [8] cannot
be observed in the spectrum at 300 K owing to: (i) an
overlapping with the f–d bands, (ii) a small energy gap
2
2
Luminescence decay curves have been recorded with a
Tektronix model TDS 3052 digital oscilloscope following
the selective excitation by a Continuum Surelite I optical
parametric oscillator (OPO), pumped by a third harmonic of a
Nd:YAG laser and detected by a photomultiplier with S-20 or
S-1 photocatode or by an InSb semiconductor detector,
depending on the spectral region.
2
4
between the K15/2 and D5/2C2K13/2 levels and (iii) a
large electron–phonon interaction, resulting in a broadening
and a red shift of the f–f bands.
In the near infrared range one observes a number of lines
connected with transitions from the 4F5/2, 2H(2)9/2, 4I13/2, 4F3/2
,
4
4I11/2 levels to the I9/2 ground level. Since the intense lines
Fig. 2. Emission spectrum of the U3C:LaBr3 single crystal in the VIS region at 300 K, recorded with lexcZ488 nm.

M. Sobczyk et al. / Solid State Communications 137 (2006) 59–62
61
Fig. 3. Emission spectrum of the U3C:LaBr3 single crystal in the NIR region at 300 K, recorded with lexcZ488 nm.
with a maximum at 5100 cmK1 disappear by using a red filter,
the single exponential time dependence. A comparison of the
lifetimes, presented in Table 1, shows that, contrary to
expectations, the largest value does not exhibit the first excited
level 4I11/2 but 4F3/2, which may be attributed to a much smaller
transition intensity in room temperatures of the latter. The
lifetimes of both levels are smaller for U3C in LaBr3 than in
4
they should be attributed to transitions from F9/2 to the
2H(2)9/2 level. The energy-level diagram of the U3C ions doped
in the LaBr3 single crystals is presented in Fig. 4.
The lifetimes of the excited states in the visible range were
measured by applying a direct, selective excitation of the
emitting levels. For measurement in the near infrared region
the excitation wavelength was 514 nm. All decay curves follow
4
LaCl3 (4I11/2-309 ms, F3/2-505 ms) in spite of the lower by
92 cmK1 lattice vibration energy in the former matrix. In liquid
Fig. 4. Energy-level diagram of U3C ions daped in the LaBr3 single crystal. Arrows indicate abundance emission transitions at 300 K observed under 5f3/5f26d1 excitation.

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M. Sobczyk et al. / Solid State Communications 137 (2006) 59–62
Table 1
Lifetimes of main fluorescing levels of U3C in LaBrK3 at 300 K
utilization in lasers, radars and telecommunication systems.
The appearance of the 5f3/5f26d1 transitions at much lower
wavenumbers, as compared with trivalent lanthanide ions, has
an additional advantage owing to an easier excitation of the
f-electrons to these broad and intense bands, by using the laser
lines at 514 and 488 nm.
Energy levels
lexc
Lifetimes (ms)
2H11/2
Selective excitation
Selective excitation
Selective excitation
Selective excitation
514 nm
10.9G0.08
10.5G0.04
w0.1
12.0G0.04
17.0G0.05
20.1G0.09
10.0G0.03
505G3.4
309G1.5
4F9/2
4G7/2
4S3/2
4F5/2
2H(2)9/2
4I13/2
4F3/2
514 nm
Acknowledgements
514 nm
514 nm
This work was supported by the University of Wrocław,
within the grant No. 250/w/WCH/, which is gratefully
acknowledged.
4I11/2
514 nm
helium temperatures the lifetime of the 4I11/2 level is markedly
4
extended (in the LaCl3 host up to 770 ms) and that of F3/2 is
somewhat shorter [9–11]. One may also notice that in the
LaBr3 host crystals the lifetimes of levels in the visible range
are larger.
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