The quadratic Jahn-Teller interaction of a triply degenerate $T$ electronic term in an $O_{ h}$ complex with ${\epsilon }_g$ and ${\tau }_{2g}$ modes has been investigated. The resulting adiabatic potential-energy surfaces show tetragonal and orthorhombic or trigonal minima coexisting for reasonable values of the appropriate parameters. The effect of the spin-orbit interaction on a ${}_{}{}^3{}_{}{}^{}T$ term has also been considered. On this basis a comprehensive model for the interpretation of the phenomenology of alkali-halide phosphors luminescence is proposed.

• Received 19 March 1974

DOI:https://doi.org/10.1103/PhysRevB.11.3052