1
236
G. Oczko, L. Macalik / Polyhedron 29 (2010) 1231–1236
can be neglected for these ions. The opposite relation was observed
Vibronic components are very clearly seen as sidebands or addi-
tional very weak lines in the low temperature absorption spectra.
Assignments of particular vibronic components, made using the
IR and Raman data, indicate that they correspond mainly to the
stretching m(Ln–Cl) and bending d(O–Ln–O) or d(Cl–Ln–O) vibra-
tions. It seems that these low wavenumber modes play an impor-
3
+
for Er chloride. The change of the R value with the decrease of the
3
+
Ln ionic radius (see Table 5) indicates significant differences in
the vibronic coupling strength along the lanthanide series in the
chlorides studied, but these changes are not monotonic. The fluctu-
ations are the same as those observed for many other systems [27],
in spite of the ionic character of the lanthanide chloride crystals,
for which the vibronic coupling strength is less than expected for
compounds with covalent bonds. For example, de Mello Donega
tant role in the electron–phonon coupling.
References
3
3
3+
observed R = 0.9 ( H
4 0 2 2
? P ) for the Pr ion in Y O S:Pr with a
3
3
[1] J.-C.G. Bünzli, in: J.-C.G. Bünzli, G.R. Choppin (Eds.), Lanthanide Probes in Life,
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covalent bond [25b], while we determined R = 0.58 ( H
for a Pr ion in the PrCl
ted as a quantitative estimation of the vibronic coupling. Thus, the
vibronic coupling strength that we observed in lanthanide chloride
4
0
? P )
3
+
3
ꢀ7H
2
O crystal [6]. The R values can be trea-
[
2] J. Wang, P.A. Tanner, J. Luminesc. 128 (2008) 1846.
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[5] O. Carugo, C. Bisi Castellani, Inorg. Chim. Acta 191 (1992) 115.
[
3+
3+
crystals is rather high for heavier ions such as Dy and Er and
[
6] G. Oczko, L. Macalik, J. Legendziewicz, J. Hanuza, J. Alloy Compd. 380 (2004)
327.
3
+
3+
much lower for Pr and Nd ions (R = 0.41 and 0.99, for the hyper-
[
[
[
7] A. Habenschuss, F.H. Spedding, Cryst. Struct. Commun. 7 (1978) 535.
8] A. Habenschuss, F.H. Spedding, Cryst. Struct. Commun. 9 (1980) 71.
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sensitive transitions of the latter ions [6]).
4
. Conclusions
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[
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0 (1996) 431.
12] J. Legendziewicz, J. Alloy Compd. 300–301 (2000) 71. and citations therein.
9
Ln3+ ions occupy one low symmetry site in the structure of
[
DyCl
3
ꢀ6H
2
O, HoCl
3
ꢀ6H
2
O and ErCl
3
ꢀ6H
2
O. The number of electronic
[13] (a) J. Legendziewicz, K. Bukiety n´ ska, G. Oczko, J. Inorg. Nucl. Chem. 43 (1981)
393;
b) J. Legendziewicz, Wiadomo s´ ci Chem. 42 (1988) 605.
14] R.B. Judd, Phys. Rev. 127 (1962) 750.
[15] G.S. Ofelt, J. Chem. Phys. 37 (1962) 511.
[16] W.T. Carnall, P.R. Fields, K. Rajnak, Chemistry Division Report, 1967.
2
(
components observed in the absorption spectra measured at 4.2 K
is compatible with that expected for these systems.
Analysis of the low temperature spectra, especially in the region
of the I
the presence of ion-pair interactions. These interactions lead to the
presence of two groups of components separated by 74 cm . The
same behaviour was observed previously for chlorides and bro-
mides of light lanthanides [6] in the region of the
[
5
5
5
5
8
? F
2
and I
8
? F
3
transitions for HoCl
3
2
ꢀ6H O, indicates
[
[
17] W.T. Carnall, P.R. Fields, K. Rajnak, J. Chem. Phys. 49 (1968) 4412.
18] A.A. Kaminskii, Laser Crystals, their Physics Properties, Springer-Verlag, Berlin,
Heidelberg, New York, 1981 (Chapter 4).
ꢂ1
[
19] G. Oczko, J. Mol. Struct. 519 (2000) 131.
4
2
[20] G. Oczko, P. Starynowicz, J. Mol. Struct. 523 (2000) 79.
21] M.P. Hehlen, H. Riesen, H.U. Güdel, Inorg. Chem. 30 (1991) 2273.
I
9/2 ? P1/2
[
3
+
3
3
3+
(
for Nd ) and
H
4
? P
0
(for Pr ) transitions, for which two
[22] D.A. Rozmanov, O.V. Sizova, M.Yu. Skripkin, K.A. Burkov, Spectrochim. Acta A
62 (2005) 92.
ꢂ1
groups of bands separated by about 100 cm
observed.
were clearly
[
[
23] S.E. Lappi, B. Smith, S. Franzen, Spectrochim. Acta A 60 (2004) 2611.
24] I.K. Ortega, R. Escribano, D. Fernández-Torre, V.J. Herrero, B. Maté, M.A.
Moreno, Chem. Phys. Lett. 396 (2004) 335.
The intensity decrease of some transitions with decreasing tem-
perature was observed for the Ho3 and Er ions in the lanthanide
chloride crystals. The same behaviour had also been noticed previ-
ously for chlorides and bromides of light lanthanides [6], and it was
attributed to the electron–phonon coupling and/or depopulation of
the Stark components of the ground state multiplet. This fact dem-
onstrates the contribution of the vibronic mechanism to the inten-
sities of electronic transitions.
+
3+
[25] (a) G. Blasse, Int. Rev. Phys. Chem. 11 (1992) 71;
(
(
b) C. de Mello Donega, A. Meijerink, G. Blasse, J. Phys. Condens. Matter 4
1992) 8889.
[
26] G. Oczko, J. Mol. Struct. 608 (2002) 17.
[27] (a) A.M. Hellwege, Ann. Phys. (Leipzig) 40 (1941) 529;
b) W.F. Krupke, Phys. Rev. 145 (1966) 325.
(