Locations and assignments of crystal-field levels in low-temperature spectra are reported for Eu3+ in the europium double nitrate system [Eu2M3(NO3)12⋅24H2O with M=Mg, Zn]. These energy levels are assigned from the polarized luminescence and the polarized absorption measurements on single crystals at 77 K. The arrangement of the oxygen atoms around the europium ion has approximate icosahedral symmetry and we have tried to find out whether the spectroscopic properties of Eu2M3(NO3)12⋅24H2O reflects this pseudosymmetry, even though the site symmetry of the europium ion is C3. Quantitative crystal-field calculations have first been performed assuming a C3v symmetry which is close to icosahedral. The levels are analyzed in terms of 20 free-ion and 6 crystal-field parameters. Afterwards it is examined how far the C3v parameters can be used to approximate the C3 symmetry. In this case, three additional imaginary crystal-field parameters are taken into account.
Unpolarized luminescence of UC1 4 powder immersed in a silicon matrix was measured at room temperature, at 77 Κ and at 4.2 K. 2S+1 Lj levels were identified assuming D 2 d symmetry for UCI4.. The identification of the observed bands is based on comparison with the results of absorption measurements [5] and with literature data [9,10,11]. Free ion calculations for the tetravalent uranium ion were very helpful [5]. The luminescence of UF 4 as a powder, immersed in a silicon matrix, was also measured and the resulting spectra are compared with those of UC1 4 . In agreement with the crystallographic data, the luminescence data of both compounds show some striking differences. The UC1 4 emission spectra are, even at ambient temperature, far more detailed than those of UF 4 .For UCI4 the obtained results were compared to the emission data of other dodecahedral U 4+ compounds [9,11]. Despite the difference in the experimental conditions, parts of the spectra show comparison concerning the position of the bands and the intensity distribution.with a KBr pellet [5]. The only difference observed is the position of the base line.
The multipolar character of transitions in lanthanide double nitrates is stressed, thereby demonstrating the effect of small deviations from an icosahedral symmetry on the fluorescence and absorption properties. Polarized absorption spectra of Nd3+ in Nd2Mg3(NO3)12⋅24H2O have been recorded between 11 600 and 28 900 cm−1 at 77 and at 4.2 K. Supplementary data were obtained by fluorescence measurements. The energy level scheme was obtained by diagonalizing a Hamiltonian describing the free ion parameters including two and three body configuration interactions, as well as the crystal field operator. Calculations were performed using the complete basis of 364‖αSLJM〉 kets of the 4f3 configuration of Nd3+. A set of free ion and crystal field parameters have been calculated with an rms deviation of 35 cm−1 with respect to 41 experimentally determined levels. The composition of the wave functions has further been checked by a calculation of the intensities for both magnetic and induced electric dipole transitions. This last mechanism, described by the Judd–Ofelt theory, introduces a set of phenomenological Bλkq parameters. The calculations of the dipole strength were done in order to underline the multipolar character of the crystal field lines of some 2S+1LJ multiplets in the visible region of the spectrum as was also noticed on the base of the selection rules. This work gives the first intensity calculation on lanthanides in double nitrates. These compounds are involved in many ionophoric complexes of lanthanides [J.-C. G. Bünzli, Handbook Phys. Chem. Rare Earths 9, 321 (1987)].
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