Absorption spectrum and crystal-field analysis of U4+ ions in CsCdBr3 single crystals

Single crystals of U4+:CsCdBr3 were grown by the Bridgman-Stockbarger technique. It has been assumed, that U4+ ions are substituting two Cd2+ ions and possess the C3v site symmetry. Thirty seven energy levels, located between 4000 and 25,000 cm−1 and encompassing all but the 1S0 multiplet, were assigned from 7 K absorption spectra. The symmetry of the levels were determined on the basis of the observed small splitting of the Γ3 doublets as well as by a comparison of low temperature absorption spectra of the U4+:CsCdBr3 with that previously reported for U4+ in Cs2UBr6 and Cs2ZrBr6 single crystals. A crystal-field analysis was performed by fitting eight atomic (in the orthogonal formalism) and 6 crystal-field parameters to the experimental Stark levels with an r.m.s. deviation of 100 cm−1. The obtained values of the Hamiltonian parameters are discussed and compared with those reported in previous analyses of U4+ ions. The relatively strong crystal field, resulting in Nv = 8530 cm−1 proves that in the CsCdBr3 crystals the U4+ ions are located at a high symmetry site.