FCenter in Cesium Fluoride: Optical Absorption Properties

Studies of the well-resolved triplet line shape of the $F$ band in cesium fluoride and its temperature dependence, magnetic circular dichroism, and stress-induced behavior are reported. The results are in accord with the picture proposed by Moran, in which the triplet structure results from a combined spin-orbit coupling and Jahn-Teller effect in the excited states, although an accurate numerical calculation of the line shape predicted by his adiabatic model shows certain features not found experimentally. The circular-dichroism results show that the contribution of the ${\Gamma }_{1g}$ lattice modes to the $F$-band second moment is ≅15%. This relatively weak coupling, taken along with the spin-orbit stabilization of the ${\Gamma }_{3g}$ and ${\Gamma }_{5g}$ mode interactions, results in the component bands of the line shape being quite narrow. These narrow bands are comparable in width to optical-phonon energies in cesium fluoride, so that discrete optical-phonon transitions are observed in the $F$ band.