Dynamic Jahn-Teller Effect in theT23Excited Term ofAl2O3:V3+

Abstract

We report high-resolution measurements of the structure near the electronic origin of the ${}_{}{}^3{}_{}{}^{}T_1^{}{}_{}{}^{}\to {}_{}{}^3{}_{}{}^{}T_2^{}{}_{}{}^{}$ absorption band of ${\mathrm{V}}^{3+}$ in ${\mathrm{Al}}_2$ ${\mathrm{O}}_3$. The structure is explained in terms of Ham's theory of the dynamic Jahn-Teller effect. The trigonal field of ${\mathrm{Al}}_2$ ${\mathrm{O}}_3$ is partially quenched, being effectively reduced by a factor of 45 in the lowest vibronic level of the Jahn-Teller distorted ${}_{}{}^3{}_{}{}^{}T_2^{}{}_{}{}^{}$ term. First-order spin-orbit coupling is quenched, but second-order effects arising from interaction with terms of the $d^2$ configuration are important. This is the first reported observation of the quenching of off-diagonal operators (the "Ham effect") other than angular momentum. The anomalous splitting of the ${}_{}{}^3{}_{}{}^{}T_1^{}{}_{}{}^{}\to {}_{}{}^3{}_{}{}^{}T_2^{}{}_{}{}^{}$ band maximum is discussed, but no very satisfactory explanation is found.