Optical absorption of s2-configuration ions in alkali halide crystals—IV: Line shape of the C band in Sn2+-doped crystals

The line shape of the C band in the alkali halide phosphors KBr:Sn²⁺, RbBr:Sn²⁺, and RbCl:Sn²⁺ has been measured as a function of temperature between about 15 K and room temperature. In contrast to earlier measurements on In⁺-doped phosphors, the C band shows a well-marked triplet structure over the whole temperature range. This triplet structure cannot be accounted for solely in terms of the dynamical Jahn-Teller effect without assuming a very large temperature-dependence for the coupling constant to vibrational modes of trigonal symmetry. The temperature-dependence both of the second moment of the line shape and of the separation between the components of the C band, suggests that there is a contribution to the splitting of the C state from a lowering in the symmetry of the static crystal field and a model which includes such a static splitting in addition to the dynamical Jahn-Teller effect provides a good representation of the experimental line shapes.