Infrared and visible luminescence spectra of MoCl₆³⁻and MoBr₆³⁻in cubic elpasolite crystals

The visible and near infrared luminescence spectra of MoCl6 3- in Cs2NaMCl6 (M=Sc, Y, In) and MoBr6 3- in Cs2NaYBr6 have been measured between 15 000 cm-1 and 3000 cm-1 at liquid helium temperatures. Comparison with new electronic absorption, infrared and Raman spectra have enabled five luminescence transitions between the states derived from the t 2g 3 configuration to be assigned unambiguously. Each electronic transition shows extensive vibronic structure which can be analysed to yield the vibrational frequencies of the MoX 6 3- ion in each state. The spectra are strongly influenced by resonant interactions between the MoX 6 3- ion and the internal and lattice modes of the host lattices and there is an enormous variation in the intensities of the vibronic origins.