Tetragonal-Field Splittings of Levels in MgO:Cr3+

Detailed ground-state and selective-excitation traces reveal new ${}_{}{}^2{}_{}{}^{}T_1^{}{}_{}{}^{}$ and ${}_{}{}^2{}_{}{}^{}T_2^{}{}_{}{}^{}$ levels in MgO: ${\mathrm{Cr}}^{3+}$. Computer diagonalizations are carried out to confirm the identity of the absorbing system. Detailed perturbation-loop calculations, which agree with results of the diagonalization, help to determine the causes of level splittings. Improved tetragonal-field parameters are given. The ${}_{}{}^2{}_{}{}^{}T_2^{}{}_{}{}^{}$ levels are assigned to the vacancy or pair-vacancy systems, whereas the ${}_{}{}^2{}_{}{}^{}T_1^{}{}_{}{}^{}$ levels are assigned to the cubic system. Assignment of other features to the ${}_{}{}^2{}_{}{}^{}T_1^{}{}_{}{}^{}$ levels of the vacancy system is tentative.