Radiation from theT24State ofCr3+in Ruby and Emerald

Abstract

The first appreciable decrease in the lifetime of the ${}_{}{}^2{}_{}{}^{}E$ state of ${\mathrm{Cr}}^{3+}$ in ruby and emerald as the temperature is raised is shown to be the result of populating the shorter-lived ${}_{}{}^4{}_{}{}^{}T_2^{}{}_{}{}^{}$ level in thermal equilibrium with the metastable ${}_{}{}^2{}_{}{}^{}E$. The direct transition from the ${}_{}{}^4{}_{}{}^{}T_2^{}{}_{}{}^{}$ to the ground ${}_{}{}^4{}_{}{}^{}A_2^{}{}_{}{}^{}$ state is shown to be mostly radiative. In both crystals, the emission peak of the ${}_{}{}^4{}_{}{}^{}T_2^{}{}_{}{}^{}\leftrightarrow {}_{}{}^4{}_{}{}^{}A_2^{}{}_{}{}^{}$ transition is shifted considerably toward longer wavelength compared to the absorption peak of that transition. The reduction in lifetime and quantum efficiency at very high temperatures is also considered.