The ${}_{}{}^3{}_{}{}^{}T_{1\mu }^{}{}_{}{}^{}$ and ${}_{}{}^3{}_{}{}^{}A_{1\mu }^{}{}_{}{}^{}$ adiabatic potential energy surfaces of ${\mathrm{T}1\mathrm{}}^{+}$-type impurities in alkali halides have been computed taking into account the spin-orbit interaction and the linear and quadratic Jahn-Teller interactions with $E_g$ vibrational modes. Effects of $T_{2g}$ modes are assumed to be negligible. The inclusion of the quadratic effect leads to tetragonal nondegenerate $T$ minima with underlying trap levels, besides $X$ minima and their trap level already predicted for the linear Jahn-Teller effect. This level scheme is required in order to explain many experimental features concerning $A_T$ and $A_X$ emissions.

• Received 21 May 1973

DOI:https://doi.org/10.1103/PhysRevB.9.4448