Direct calculation of the two-photon line strength of a Gamma 1g- Gamma 1g transition in octahedral symmetry.

Abstract

Using a direct calculation, the line intensity of the two-photon $(^{7}F_{6}){\ensuremath{\Gamma}}_{1g}\ensuremath{-}{\ensuremath{\Gamma}}_{1g}(^{5}D_{4})$ transition of ${\mathrm{Tb}}^{3+}$ in the elpasolite lattice has been accounted for under third-order perturbation theory. Employing the appropriate $4{f}^{7}5d$ intermediate levels, $\ensuremath{\chi}$ and $\ensuremath{\mu}$, the transition moment has been written in terms of electric-dipole allowed transitions between the $4{f}^{8}$ and $4{f}^{7}5d$ configurations, and of the spin-orbit coupling between the intermediate states. The calculated line strength is sensitive to the locations of the intermediate-state energy levels.