On the multipolar character of some 2S+1L J transitions in Nd2Mg3(NO3)12⋅24H2O: An optical study and semiempirical crystal field analysis

Abstract

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)].