Luminescence from oxygen vacancies in MgO crystals thermochemically reduced at high temperatures

Experimental measurements and theoretical calculations are reported which may resolve some of the remaining difficulties associated with photoemission from anion vacancies in thermochemically reduced MgO crystals. The intensities of the 2.3- and 3.2-eV luminescence bands are found to be strongly influenced by both the concentrations of ${\mathrm{H}}^{-}$ ions and anion vacancies present, and also by the intensity of the ∼5.0-eV exciting light. Theoretical calculations predict that for a ${}_{}{}^1{}_{}{}^{}A_{1g}^{}{}_{}{}^{}$ relaxation of the surrounding ions the ${}_{}{}^1{}_{}{}^{}T_{1u}^{}{}_{}{}^{}$ and ${}_{}{}^3{}_{}{}^{}T_{1u}^{}{}_{}{}^{}$ electronic states of the $F$ center are almost degenerate and ∼0.05 eV above the ${}_{}{}^3{}_{}{}^{}A_{1g}^{}{}_{}{}^{}$ state. The ${}_{}{}^1{}_{}{}^{}T_{1u}^{}{}_{}{}^{}\to {}_{}{}^1{}_{}{}^{}A_{1g}^{}{}_{}{}^{}$ and the ${}_{}{}^3{}_{}{}^{}T_{1u}^{}{}_{}{}^{}\to {}_{}{}^1{}_{}{}^{}A_{1g}^{}{}_{}{}^{}$ transition energies are predicted to be 2.2 and 2.9 eV, respectively.