Spectrum analysis of U3+-doped LaBr3 single crystals. Part 1: Crystal-field analysis

Article abstract of DOI:10.1016/j.jssc.2004.10.024

Single crystals of U³⁺:LaBr₃ were grown by the Bridgman-Stockbarger technique. High-resolution polarized absorption spectra of the crystals were recorded at 4.2 K in the 4000-50,000 cm^-1 range. Sixty-four experimental crystal-field energy levels of the U³⁺ ion were fitted to a semiempirical Hamiltonian employing free-ion, one-electron crystal-field as well as two-particle correlation crystal-field (CCF) operators with an r.m.s. deviation of 28 cm^-1. The performed analysis of the spectra enabled the determination of crystal-field parameters and assignment of the observed 5f³→5f³ transitions. The effects of selected CCF operators on the splitting of some specific U³⁺ multiplets have been investigated and the obtained values of Hamiltonian parameters are discussed and compared with those reported in previous analyses.

Full text of DOI:10.1016/j.jssc.2004.10.024

ARTICLE IN PRESS
Journal of Solid State Chemistry 178 (2005) 536–544
www.elsevier.com/locate/jssc
Spectrum analysis of U3+-doped LaBr3 single crystals.
Part 1: crystal-field analysis
Ã
Marcin Sobczyk, Janusz Droz’dz’ynski , Miros"aw Karbowiak
Faculty of Chemistry, University of Wroc!aw, ul. F. Joliot-Curie 14, 50-383 Wroclaw, Poland
Received 19 May 2004; received in revised form 8 October 2004; accepted 15 October 2004
Abstract
Single crystals of U3+:LaBr3 were grown by the Bridgman–Stockbarger technique. High-resolution polarized absorption spectra
of the crystals were recorded at 4.2 K in the 4000–50,000 cmꢀ1 range. Sixty-four experimental crystal-field energy levels of the U3+
ion were fitted to a semiempirical Hamiltonian employing free-ion, one-electron crystal-field as well as two-particle correlation
crystal-field (CCF) operators with an r.m.s. deviation of 28 cmꢀ1. The performed analysis of the spectra enabled the determination
of crystal-field parameters and assignment of the observed 5f3-5f3 transitions. The effects of selected CCF operators on the
splitting of some specific U3+ multiplets have been investigated and the obtained values of Hamiltonian parameters are discussed
and compared with those reported in previous analyses.
r 2004 Elsevier Inc. All rights reserved.
Keywords: Uranium(3+); Uranium tribromide; U(3+)-doped single crystals; Crystal-field; Energy levels; Crystal-field parameters; Correlation
crystal-field parameters; Low-temperature absorption spectra
1. Introduction
level structure consistent with experimental data of the
U3+ ion. Furthermore, since the first f–d bands in these
crystals appear at about 21,000 cmꢀ1 one may suspect
that at least 20 from among the 117 crystal-field levels
included in the calculations by Paszek, were of uncertain
origin. Among the so far obtained U3+-doped single
crystals only LaCl3 [3–5], LaBr3 and LiYF4 [6] exhibit a
suitable site symmetry for precise energy-level
tructure investigations with application of electric and
magnetic–dipole transition selection rules. Crystal-
field analyses of U3+:Cs2NaYBr6 [7] single crystals as
well as UCl3 and UBr3 polycrystalline samples are also
available [8].
The aim of the investigations has been the perfor-
mance of a comprehensive spectroscopic analysis of
U3+ ions doped in LaBr3 single crystals. The first part of
the analysis presents crystal-field calculations with the
inclusion of two-particle correlation crystal-field (CCF)
operators in order to obtain a reliable set of atomicand
crystal-field parameters. The investigations of upconver-
sion and luminescence properties of the crystals will be
presented in the second part.
The first analysis of this system has been presented in
the Ph.D. thesis of A.P. Paszek at the Johns Hopkins
University in Baltimore [1]. For reasons unknown to us
the results have not been published, with the exception
of atomicand rcystal-field parameters, presented in a
review article by Carnall [2]. However, from this set of
parameters we were not able to reproduce an energy
2. Experimental
Uranium(3+)-doped single crystals of LaBr3 with
nominal 0.1, 0.05 and 0.01 mol% uranium concentration
were grown in silica ampoules by the Bridgman–Stock-
barger method. LaBr3 was synthesized from La2O3
Ã
Corresponding author. Fax: +48 71 238 23 48.
E-mail address: jd@wchuwr.chem.uni.wroc.pl (J. Droz’dz’ynski).
0022-4596/$ - see front matter r 2004 Elsevier Inc. All rights reserved.
doi:10.1016/j.jssc.2004.10.024

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M. Sobczyk et al. / Journal of Solid State Chemistry 178 (2005) 536–544
537
Fig. 1. Survey absorption spectrum of U3+: LaBr3 at 4.2 K.
(99.999%) by the ammonium bromide route and
includes the following terms:
sublimed under high vacuum. Uranium tribromide was
prepared according to the procedure reported in Ref. [9].
Polarized absorption spectra of the LaBr3:U3+ single
crystals were recorded on a Cary 5E NIR-Vis-UV
spectrophotometer in the 4000–50,000 cmꢀ1 range
(Fig. 1). Luminescence spectra have been obtained upon
excitation of the U3+ ions in this crystal by an argon ion
laser (0.24 W at wavelength 514 nm, 19455 cmꢀ1).
Luminescence was dispersed by a 1-m double-grating
monochromator, detected by the Hamamatsu R-928
photomultiplier, averaged by the Stanford model SRS
250 boxcar integrator and stored in a PC computer. For
low-temperature measurements a continuous flow he-
lium cryostat (Oxford model CF 1204) equipped with a
temperature controller was used.
^
^
^
^
H ¼ HA þ HCF þ HCCF
:
(1)
^
The free-ion Hamiltonian HA [11] contains the isotropic
^
(atomic) parts of H and is defined as
X
k
^
^
^
HA ¼ Eave
þ
F ðnf ; nf Þf k þ z5f ASO
k¼2;4;6
^
^ ^
^
þ
þ
aLðL þ 1Þ þ bGðG2Þ þ gRðR7Þ
X
X
X
i
j
k
P pk
^
^
^
T ti þ
M mj þ
ð2Þ
i¼2;3;4;6;7;8
j¼0;2;4
k¼2;4;6
where Eave is the spherically symmetric one-electron part
of the Hamiltonian, Fkðnf ; nf Þ and z5f represent the
radial parts of the electrostatic and spin–orbit interac-
^
^
tions, while f k and ASO are the angular parts of these
interactions, respectively. The a, b and g, parameters are
associated with the two-body correction terms. GðG2Þ
and GðR7Þ are Casimir operators for the G2 and R7
groups. L is the total orbital angular momentum. The
three-particle configuration interaction is expressed by
3. Energy level calculations
Crystal-field calculations have been performed by
applying the f-shell empirical program, delivered by
M.F. Reid (University of Canterbury, New Zealand)
and running on PC under the Linux Mandrake
operating system. The effective operator model
was used for the analysis of the obtained data [10].
The eigenvectors and eigenvalues of the crystal-
field levels were obtained by
diagonalization of the combined free-ion and
crystal-field energy matrices. The applied Hamiltonian
i
i
i
^
^
T t ði ¼ 2; 3; 4; 6; 7; 8Þ; where T are parameters and ti
are three-particle operators.
The electrostatically correlated spin–orbit perturba-
tion is represented by the Pk parameters and those of the
spin–spin and spin-other-orbit relativistic corrections by
the Mj parameters. The operators associated with these
a
simultaneous
j
k
^
^
parameters are designated by m and p ; respectively.

ARTICLE IN PRESS
M. Sobczyk et al. / Journal of Solid State Chemistry 178 (2005) 536–544
538
^
The HCF term of the Hamiltonian represents the one
of 64 experimental data only. In order to reduce the
number of this CCF parameters we have followed the
procedure presented by Li and Reid [14] in an analysis
of some Nd3+-doped crystals and we applied it in a
recent analysis of U3+:LaCl3 [5] low-temperature
absorption spectra. It has been shown that the inclusion
of only a few of the parameters have markedly improved
the fits and could resolve problems with poorly fitted
levels by the one-electron crystal-field operator HCF. In
the performed spectrum analysis of U3+:LaBr3 the most
problematicmultiplets were 2H29/2 and 4F5/2 for which a
considerable discrepancy between the calculated and
experimental splitting values has been found. Similarly,
as in our previous analysis [5], we have stated that only
the three G410A;0; G140B0 and G240 fourth-rank parameters
and one G610B0 sixth-rank parameter were statistically
significant.
LaBr3 crystallizes in the UCl3-type structure (space
group P63/m, No. 176) with the C3h point symmetry of
the La3+ site [15]. The La3+ ions are coordinated by
nine Brꢀ ions in the shape of a tricapped trigonal prism.
The U3+ ions randomly substitute for La3+ site. No
hints of clustering or the occupation of other lattice sites
could be detected. The crystal field splits the atomic
states of the 5f3 configuration into Kramers doublets
which may be classified as having the E1=2ðG7 þ G8Þ;
E3=2ðG11 þ G12Þ or E5=2ðG9 þ G10Þ symmetry in the C3h
double-rotation group. The selection rules for the
electron crystal-field and is defined as [10]
X
^
HCF
¼
BkqCðqkÞðiÞ;
(3)
k;q;i
where CðqkÞðiÞ is a spherical tensor of rank k and Bkq are
crystal-field parameters. The crystal-field Hamiltonian
for the C3h site is expressed as follows:
HCF ¼ B20C20 þ B40C04 þ B60C06 þ B66ðCꢀ6 6 þ C66Þ
6
þ B06iðC6ꢀ6 þ C66Þ:
ð4Þ
Depending on an arbitrary choice of the coordinating
system the B66 parameter may be either complex, purely
real or purely imaginary. In the coordinate system
chosen in this analysis, the imaginary part of B66
vanishes. The last term of the complete Hamiltonian
represents the correlated two-electron crystal-field inter-
actions. Following Reid [12] the parameterization of
these interactions may be written in Judd’s notation [13]
as a set of GKiQ parameters:
X
ðKÞ
K
GiQgiQ
^
HCCF
^
¼
;
(5)
i;K;Q
where K runs through the even integers from 0 to 12,
^
ðKÞ
i distinguishes different giQ operators with identical K,
and Q is restricted by the crystal field symmetry.
Since there appear, 41 additional independent para-
meters one cannot include all of them in a fit with a set
4
2
4
Fig. 2. Absorption transitions in p and s polarization, from the I9/2 ground state to the excited H29/2 and F9/2 multiplets of the U3+:LaBr3 and
U
3+:LaCl3 single crystals. The insert gives selection rules for electric-dipole and magnetic-dipole transitions of U3+:LaBr3 (site symmetry C3h). s and
p correspond to E?c and E || c, respectively.

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539
electric–dipole and magnetic–dipole transitions are
given in the insert of Fig. 2. The lowest crystal-field
value. The P2 parameter was varied while P4 and P6
were kept at a constant ratio to P2. For comparison we
have also performed a fit without the CCF parameters.
The complete parameter sets for both fits are presented
in Table 1. The experimental and calculated energy level
values are presented in Table 2. In the analysis
performed by Paszek [1] of the U3+:LaBr3 absorption
spectrum, were included 117 experimental crystal-field
levels, positioned up to 25,723 cmꢀ1. Since, above
21,000 cmꢀ1, the f–f bands are obscured by strong and
broad f–d bands, these results may not be considered as
fully reliable.
4
level of the ground I9/2 multiplet manifold of U3+ has
the E5=2 symmetry. Since the transitions observed in
liquid helium temperature originate only from this level
they must terminate on the E3=2 or E1=2 excited level for
s polarization and E1=2 for p polarization. Hence, the
selection rules allow for an unambiguous assignment of
the irrep labels of all lines observed in the spectrum. The
incompletely diminished intensity of the forbidden
transitions observed in Fig. 2 is probably caused by a
small distortion of the C3h symmetry of the U3+ ion.
In the fitting procedure, 64 experimental energy levels
have been determined and assigned from 5 K unpolar-
ized as well as s- and p-polarized absorption spectra.
The levels were fitted to the parameters of the
phenomenological Hamiltonian (1). In the final fitting
procedure 14 atomic parameter, 4 one-electron CF
parameters and 4 CCF parameter were freely varied.
The initial values of the free-ion and crystal field
parameters were taken from the previous analyses
[4,5]. The T8 and M0 parameters were kept at a constant
In the calculations the complete (364 ꢁ 364) SLJMJ
matrix has been diagonalized. The quality of the fits
were determined using the r.m.s. deviation (in cmꢀ1
defined as
)
À
!
Á
1=2
2
X
Eexp : ꢀ Ecalc
ðn ꢀ pÞ
r:m:s: ¼
;
(6)
where n is equal to the number of levels and p is the
number of parameters that are varied freely. In order to
Table 1
Hamiltonian parameters (in cmꢀ1) obtained from crystal-field (CF) and correlation crystal-field (CCF) analyses
Parametera
U3+:LaBr3
CF
UBr3 [8]
CCF
U3+:LaCl3 [5]
CCF
U3+:LaBr3 [1]
CF
CCF
Eavg
F2
F4
F6
z
19,313(56)
38,085(203)
31,442(232)
22,310(244)
1620(15)
29(7)
19,339(50)
38,528(180)
31,732(209)
22,416(217)
1621(13)
29(6)
19,213(60)
37,931(216)
30,281(256)
20,536(257)
1606(16)
29(7)
19,426(34)
38,459(128)
30,786(161)
19,981(174)
1614(11)
31(4)
38,332
32,959
22,563
1602
29
a
b
g
ꢀ880(36)
1452(126)
538(99)
ꢀ893(33)
1391(113)
426(87)
ꢀ864(46)
1690(136)
347(105)
17(28)
ꢀ886(34)
1928(93)
388(68)
ꢀ918
[1200]
[380]
49
T2
T3
T4
T6
T7
T8
M0
P2
B02
75(29)
234(47)
56(23)
250(42)
39(22)
154(33)
252(48)
236
ꢀ419
369
ꢀ55(63)
496(53)
[300]
ꢀ159(52)
489(42)
[300]
ꢀ303(64)
292(50)
[300]
ꢀ233(38)
401(35)
[300]
(350)
[0.67]
—
[0.6720]
1411(71)
372(38)
[0.672]
1330(62)
373(33)
[0.672]
1616(76)
350(43)
[0.672]
1491(52)
312(33)
407
B04
B06
B66
G410A;0
G410B;0
G42;0
ꢀ220(66)
ꢀ1252(61)
797(52)
ꢀ207(68)
ꢀ1174(55)
855(45)
ꢀ562(78)
ꢀ1568(69)
770(54)
ꢀ459(66)
ꢀ1462(55)
1027(47)
1001(98)
484(91)
ꢀ539
ꢀ1226
590
926(96)
969(135)
744(103)
793(207)
ꢀ1399(126)
307(90)
1431(187)
ꢀ1454(109)
64
817(181)
ꢀ1590(108)
67
G610B;0
N
r.m.sb
64
33
46
117
27
28
31
29
aThe parameters are defined in Section 3. Values in brackets indicate parameter errors. Parameters in square brackets were kept constant during
the fitting procedure. P4 ¼ 0:75 P2, P6 ¼ 0:5 P2.
bStandard deviation. See equation (6).

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540
Table 2
Electronic states, symmetry labels, experimental and calculated energy levels of U3+:LaBr3
SLJ multipleta
Irrep.
Det.b
CF
CCF
Exptl energy
(cmꢀ1
Calc. energy
(cmꢀ1
Eexp: ꢀ Ecalc (cmꢀ1
)
Calc. energy
(cmꢀ1
)
Eexp: ꢀ Ecalc
(cmꢀ1
)
)
)
4I9/2
E5/2
E1/2
E3/2
E5/2
E3/2
L
L
L
L
L
0
190
200
367
392
49
175
195
372c
360c
ꢀ49
15
45
210
195
343
362
ꢀ45
ꢀ20
5
5
ꢀ5
32
24
30
4I11/2
E3/2
E1/2
E5/2
E1/2
E3/2
E5/2
A
A
L
4422
4474
4495
4514
4522
4575
4424
4455
4506
4517
4529
4566
ꢀ2
19
4426
4463
4495
4529
4534
4559
ꢀ4
11
ꢀ11
ꢀ3
ꢀ7
9
0
A
A
L
ꢀ15
ꢀ12
16
4F3/2
4I13/2
E1/2
E3/2
A
A
7009
7034
7005
7030
4
4
7007
7025
2
9
E1/2
E3/2
E1/2
E5/2
E1/2
E3/2
E5/2
A
A
A
8114
8181
8213
8117
8203
8216
8252
8268
8307
8369
ꢀ3
ꢀ22
ꢀ3
8116
8195
8218
8240
8275
8310
8363
ꢀ2
ꢀ14
ꢀ5
A
8260
ꢀ8
ꢀ15
2H29/2
E5/2
E3/2
E3/2
E1/2
E5/2
9469
9481
9610c
9588
9698
9346
9434
9612
9650
9670
A
A
A
9406
9600
9696
ꢀ75
ꢀ10
108
ꢀ28
ꢀ12
46
4F5/2
E5/2
E3/2
E1/2
9829
9842
9877
9817
9859
9866
A
A
9833
9893
ꢀ9
ꢀ26
16
27
4G5/2
+
E1/2
E1/2
E3/2
A
A
A
11086
11129
11144
11059
11124c
11121c
27
5
11047
11129
11134
39
0
4S3/2
4F7/2
+
+
23
10
4I15/2
E5/2
E3/2
E1/2
E3/2
E5/2
E1/2
E5/2
E1/2
E3/2
E5/2
E1/2
E3/2
E3/2
E5/2
11168
11184
11227
11423
11434
11444
11504
11506
11559
11652
11676
11747
11835
11937
11160
11184
11213
11404
11409
11442
11505
11504
11549
11616
11671
11737
11822
11920
A
A
A
11179
11243
11395
ꢀ5
16
ꢀ5
30
ꢀ29
ꢀ9
A
A
11425
ꢀ19
ꢀ17
11548
11565
46
6
44
17
A
11689
13
18
4G7/2
E5/2
E3/2
E1/2
E5/2
L
13142
13217
13238
13188
13203
13306c
13248c
ꢀ46
14
13183
13210
13298c
13245c
ꢀ41
7
A
A
ꢀ68
ꢀ61
4F9/2
E5/2
E1/2
E3/2
E5/2
E3/2
14577
14595
14630
14648
14665
14535
14610
14633
14628
14690
A
A
14607
14622
12
ꢀ8
ꢀ3
ꢀ11

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541
Table 2 (continued )
SLJ multipleta
Irrep.
Det.b
CF
CCF
Exptl energy
(cmꢀ1
Calc. energy
(cmꢀ1
Eexp: ꢀ Ecalc (cmꢀ1
)
Calc. energy
(cmꢀ1
)
Eexp: ꢀ Ecalc
(cmꢀ1
)
)
)
2H21/2
E1/2
E3/2
E1/2
E3/2
E5/2
E5/2
A
A
A
A
15352
15362
15393
15405
15330
15366
15417c
15391c
15460
15554
22
ꢀ4
15358
15349
15440c
15374c
15372
15466
ꢀ6
13
ꢀ24
14
ꢀ47
31
4D13/2
E1/2
E3/2
A
A
15723
15776
15757
15762
ꢀ34
15749
15758
ꢀ26
14
18
2K13/2
E1/2
E3/2
E5/2
E1/2
E5/2
E3/2
E1/2
A
A
15863
15994
15852
16020c
16010c
16027
16074
16094
16132
11
ꢀ26
15844
16003c
15965c
16050
16032
16133
16170
19
ꢀ9
A
16023
ꢀ4
ꢀ27
4D1/2
E1/2
E5/2
E3/2
E3/2
E5/2
E1/2
E3/2
E1/2
E5/2
E5/2
A
16251
16264
16734
16753
16792
16849
16851
16931c
16914c
17003
17056
ꢀ13
16246
16703
16758
16794
16841
16837
16916
16920
16981
17029
5
4G9/2
+
2G17/2
A
A
16796
16807
43
15
38
13
A
A
A
16870
16886
16914
19
ꢀ45
0
33
ꢀ30
ꢀ6
4D5/2
E5/2
E3/2
E1/2
17257
17326
17330
17258
17327
17338
A
17322
ꢀ4
ꢀ5
2K15/2
E1/2
E3/2
E1/2
E3/2
E5/2
E1/2
E3/2
E5/2
A
A
A
A
18363
18394
18414
18580
18356
18396
18458
18550
18572
18604
18641
18673
7
ꢀ2
18356
18405
18443
18545
18556
18608
18642
18669
7
ꢀ11
ꢀ29
35
ꢀ44
30
A
A
18618
18645
14
4
10
3
4D23/2
E1/2
E3/2
A
A
19006
19020
19004
19014
2
6
19002
19022
4
ꢀ2
2H111/2
E1/2
E3/2
E1/2
A
A
A
19600
19625
19706
19618
19643
19659
ꢀ18
ꢀ18
47
19621
19643
19685
21
ꢀ18
21
aNominal spectroscopic symbols for the energy state(s) associated with the group of levels.
bValues determined from analysis of luminescence (L) or absorption (A) spectra.
cIndicate levels for which the order of the calculated values was reversed.
compare the magnitudes of the total crystal field
strength the scalar parameter [16]
4. Results and discussion
In the 4000–19750 cmꢀ1 absorption range relatively
sharp and well-separated bands of intraconfigurational
5f3-5f3 transitions have been observed (Fig. 1). At
higher wave numbers the bands are obscured by strong
5f3-5f26d1 transitions. Since the absorption spectrum is
"
#
1=2
X
4p
ð2k þ 1Þ
2
Nv ¼
ðBkqÞ
(7)
k;q
has been applied.

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542
similar to those of U3+:LaCl3 [5] and UBr3 [8] a
comparison of the spectra enabled an unambiguous
identification of most of the recorded crystal-field bands.
In Fig. 2, absorption transitions in p and s polarization,
standard deviation for the overall fit decreases from 33
to 28 cmꢀ1
Most values of the Hamiltonian parameters obtained
in this analysis (Table 1) are generally similar to those
reported in our previous analysis of U3+:LaCl3 [4] and
UBr3 [6]. One may notice somewhat larger values for the
Fk parameters and almost the same for z5f with
reference to those of U3+:LaCl3 and UBr3. Besides,
one observes significant differences in the values of g and
some of the three-body Tk parameters. An increase in
metal-ligand covalency results in an increase of the
average distance between the valence electrons, which in
turn leads to a decrease of the Coulomb repulsion. At
the same time the delocalization of the electron density
leads to a reduction of the orbital angular momentum
and consequently to a decrease of the spin–orbit
coupling values. Thus, smaller values of the Fk and z
parameters should be expected for U3+:LaBr3, which
remain in disagreement with the results of our calcula-
tions. However, one should emphasize, that also in a
crystal-field analysis of Er3+ ions diluted in Cs3Lu2Cl9,
Cs3Lu2Br9 and Cs3Y2I9 single crystals, the obtained
values of the Fk parameters do not exhibit an expected
steady decrease along the Cl–Br–I series of compounds
[17]. We have attributed a similar inconsistency, noticed
for the F4 parameter in the CF analysis of
U3+:Cs3Lu2Cl9 and U3+:Cs3Y2I9 single crystals [18] to
uncertainties in the determination of the configuration
interaction as well of some minor atomic parameters.
Hence, it appears, that for the observed discrepancy in
this analysis, similar factors may be responsible. Since,
between U3+:LaCl3 and U3+:LaBr3 the values of the
‘‘free ion’’ parameters should not exhibit considerable
4
2
from the I9/2 ground state to the excited H29/2 and
4F9/2 multiplets of the U3+:LaBr3 and U3+:LaCl3 single
crystals are presented. One may observe an expected red
shift and a somewhat smaller crystal-field splitting of the
bands with reference to those of U3+:LaCl3. It is worth
noting, however, that the crystal-field splitting of the
2K13/2 as well as of some other multiplets, located at
higher energies, exhibit for the bromide crystal some-
what larger values (Table 3). This irregularity may be
attributed to the proximity of the f–d states, which in
U3+:LaBr3 appear at lower wave numbers. A similar
observation have been noticed by Luthi et al. [17] in an
analysis of Er3+-doped Cs3Lu2Cl9, Cs3Lu2Br9 and
Cs3Y2I9 single crystals.
A comparison of the values of the total splitting and
the centers of gravity of the LSJ multiplets, observed in
the low-temperature spectra of U3+:LaCl3 and
U3+:LaBr3, is presented in Table 3. The energy values
4
of the crystal-field components of the I9/2 ground level
have been determined from an analysis of the emission
2
2
4
spectra originating from the K15/2, H211/2 and F9/2
levels (Fig. 3, Table 2)
The largest Ecalc–Eobs. differences equal to ꢀ75 and
108 cmꢀ1 exhibit the recorded at 9406 and 9696 cmꢀ1
2
levels of the H29/2 multiplet, respectively. The order of
the calculated value of the second one was reverse
(see Table 2.). After inclusion of the CCF parameters
the order became correct, the (Eexp.–Ecalc.) values
decrease down to 28 and 46 cmꢀ1 respectively, and the
Table 3
A comparison of the total splittings and centers of gravity (CG) of LSJ multiplets in the low temperature spectra of U3+:LaCl3 and U3+:LaBr3 single
crystals
LSJ multiplet
Total splitting
3+:LaCl3 (cmꢀ1
CG relative
U
)
U3+:LaBr3 (cmꢀ1
)
U3+:LaCl3 (cmꢀ1
)
U3+ :LaBr3 (cmꢀ1
)
4I9/2
451
164
18
392
153
25
269
4540
230
4450
4I11/2
4F3/2
7090
8279
7021
8240
4I13/2
285
383
90
249
324
76
2H29/2
9595
9912
9544
9848
4F5/2
4G5/2+4S3/2+4F7/2+4I15/2
968
111
187
159
56
834
103
156
114
53
11498
13298
14686
15455
15853
16117
16518
16941
17546
18666
19209
11445
13210
14616
15392
15749
16026
16251
16870
17329
18530
19013
4G7/2
4F9/2
2H211/2
4D13/2
2K13/2
270
0
307
0
4D1/2
4G9/2+2G17/2
4D5/2
334
73
326
80
2K15/2
4D23/2
298
12
306
14

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543
Fig. 3.
changes, one may assume that those which display such
differences, e.g. g and most of the three-body Tk
parameters, have not been correctly determined. An
additional important factor responsible for the discre-
pancy, appear to be the influence of excited configura-
tions, evidenced by the above-mentioned larger CF
splitting of U3+:LaBr3 multiplets, located at higher
wavenumbers. Since the applied Hamiltonian is repre-
senting the combined free-ion and CF interactions this
influence is not separately taking into consideration in
the calculations. Hence, some deficiencies in the CF part
may be absorbed by the free-ion part, resulting in the
appearance of disturbed values of the, e.g. Fk para-
meters, and vice versa.
The one-electron Bkq parameter values are, as expected
for a bromide system, somewhat smaller than those of
U3+:LaCl3 and UBr3 with the exception of B20 with
reference to U3+:LaCl3 and UBr3, and B66 with reference
to UBr3. The values of the CCF parameters are similar
to those determined for LaCl3, except of G42;0; which
assumed a considerably larger value.
–0.1 [19]. This may point to a stronger correlation effect
in the bromide crystal, but it may also result from a
deficiency of the applied theoretical model for a
description of CF levels of the 5f3 configuration. Hence,
the observed improvement in the adjustment of some of
these levels may result from the inclusion of additional
parameters, which just on these levels display the largest
influence.
The crystal-field of U3+:LaBr3 is somewhat weaker
than those of UBr3 or U3+:LaCl3, due to the
comparatively long La–Br distances which causes that
the particular multiplets are relatively well separated
and, except of two, do not overlap. In accordance with
this statement, the Nv total crystal-field strength
parameter (7) for U3+:LaBr3 amount to 1593 cmꢀ1
(largest total splitting value D=392 cmꢀ1) and is as
expected smaller than that for UBr3, (Nv=1923 cmꢀ1
,
,
D=411 cmꢀ1
D=451 cmꢀ1
)
.
and
U3+:LaCl3
(Nv=1904 cmꢀ1
For comparison purposes, the Bkq values should be
multiplied by ꢂ14 ꢁ (12/77)1/2 due to a differently
normalization of the CCF operators. The values of the
G140A;0=B40; G410B;0=B40; G24=B04 and G66A;0=B60 ratios calcu-
lated in this manner are equal to ꢀ0.81, ꢀ0.27, ꢀ1.25
and 0.22, respectively. Thus, the fourth-rank CCF
parameters achieve the same order of magnitude as the
one-electron parameters. The corresponding ratios for
U3+:LaCl3 are equal to ꢀ0.39, ꢀ0.19, ꢀ0.32 and 0.20,
and are larger than those of the Nd3+:LaCl3 crystals, for
which the average corrected G410A;0=B04 ratio is about
5. Conclusion
The paper presents a comprehensive crystal-field
energy level analyses of polarized low-temperature
absorption spectra of U3+:LaBr3 single crystals. The
analysis enabled the assignment of the observed 5f3-5f3
transitions and the determination of atomicand crystal-
field parameters. Including contributions from two-
electron correlation crystal-field interactions we could
eliminate major discrepancies between the calculated
2
and observed energy levels within the H29/2 multiplet.

ARTICLE IN PRESS
M. Sobczyk et al. / Journal of Solid State Chemistry 178 (2005) 536–544
544
The values of the obtained Hamiltonian parameters are
discussed and compared with those reported in previous
analyses. The obtained Fk parameters are somewhat
larger with reference to those of U3+:LaCl3, which
seems to result from difficulties in a correct determina-
tion of the configuration interaction and of some minor
atomicparameter values. The CF splitting of multiplets
located at higher than 16,000 cmꢀ1 are unexpectedly
larger for U3+:LaBr3 than for U3+:LaCl3, which may
be attributed to the influence of the proximity of the
opposite parity 5f26d1 configuration.
[2] W.T. Carnall, Absorption and luminescence spectra, in: Gmelin
Handbook of InorganicChemistry, Uranium Supplement, vol.
A5, Springer, New York, pp. 69–161.
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[4] W.T. Carnall, Systematicanalysis of the spetcra of trivalent
actinide chlorides in D3h site symmetry, ANL Report 89/39.
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Acknowledgments
[11] W.T. Carnall, G.L. Goodman, K. Rajnak, R.S. Rana, J. Chem.
Phys. 90 (1989) 3443.
This work was supported by the Polish Committee for
Scientific Research within the Project No. 7TO9A080 20
as well as by the grant No. 2530/w/WCH/04 of the
University of Wroc"aw, which is gratefully acknowl-
edged.
[12] M.F. Reid, J. Chem. Phys. 87 (5) (1987) 2875.
[13] B.R. Judd, J. Chem. Phys. 66 (1977) 3163.
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