Four emission bands related to the $A$ and $C$ excited states, $A_{T\Pi }$, $A_{T\Sigma }$, $C_{T\Sigma }$, and $C_{T\Pi }$, have been observed in KI:${\mathrm{Sn}}^{2+}$ at 4.2°K, and the degree of polarization has been studied. The results indicate that the $\Gamma _4^{}{}_{}{}^{-}$ (${}_{}{}^3{}_{}{}^{}T_{1\mathrm{u}}^{}{}_{}{}^{}$ and ${}_{}{}^1{}_{}{}^{}T_{1\mathrm{u}}^{}{}_{}{}^{}$) excited states are tetragonally distorted by a strong Jahn-Teller effect and are also perturbed by a charge-compensating vacancy located in the nearest-neighbor position.

• Received 14 December 1970

DOI:https://doi.org/10.1103/PhysRevLett.26.314