Line shape and lifetimes ofCr3+luminescence in silicate glasses

This paper describes experimental and theoretical studies of the distribution of crystal-field sites occupied by ${\mathrm{Cr}}^{3+}$ ions in silicate glasses. The effects of this site-to-site disorder on the optical band shape of ${}_{}{}^4{}_{}{}^{}$ ${\mathit{T}}_2$ ${\to }^4$ ${\mathit{A}}_2$ and ${}_{}{}^2{}_{}{}^{}$E${\to }^4$ ${\mathit{A}}_2$ transitions, luminescence decay time, and their temperature dependences are calculated and compared with experimental results. Since the distribution of the crystal-field splitting, 10Dq, includes sites having values of the energy separation E${(}^4$ ${\mathit{T}}_2$)-E${(}^2$E), which vary from positive, through zero to negative, it is necessary to take into account the effects of ${}_{}{}^4{}_{}{}^{}$ ${\mathit{T}}_2$ to ${}_{}{}^2{}_{}{}^{}$E tunneling induced by spin-orbit coupling and zero-point vibration. Good agreement is obtained between theory and experiment, giving confidence in the assumed distribution of crystal-field sites.