One-color two-photon excitation spectra of the ${}_{}{}^7{}_{}{}^{}$${\mathit{F}}_0$${\to }^5$${\mathit{D}}_0$ and ${}_{}{}^7{}_{}{}^{}$${\mathit{F}}_0$${\to }^5$${\mathit{D}}_2$ transitions of ${\mathrm{Sm}}^{2+}$ in ${\mathrm{SrF}}_2$ have been measured at low temperature and their dependences upon photon polarization analyzed. Linewidths on the order of 0.2, 0.6, and 1.0 ${\mathrm{cm}}^{\mathrm{-}1}$ are obtained for the ${}_{}{}^7{}_{}{}^{}$${\mathit{F}}_0$${\to }^5$${\mathit{D}}_0$(${\mathit{A}}_{1\mathit{g}}$), ${}_{}{}^7{}_{}{}^{}$${\mathit{F}}_0$${\to }^5$${\mathit{D}}_2$(${\mathit{E}}_{\mathit{g}}$), and ${}_{}{}^7{}_{}{}^{}$${\mathit{F}}_0$${\to }^5$${\mathit{D}}_2$(${\mathit{T}}_{2\mathit{g}}$) Stark components observed at 15 K, respectively. The ${}_{}{}^7{}_{}{}^{}$${\mathit{F}}_0$${\to }^5$${\mathit{D}}_0$(${\mathit{A}}_{1\mathit{g}}$) transition is observed to be isotropic within experimental error, while the ${\mathit{E}}_{\mathit{g}}$ and ${\mathit{T}}_{2\mathit{g}}$ components of the ${}_{}{}^7{}_{}{}^{}$${\mathit{F}}_0$${\to }^5$${\mathit{D}}_2$ transition exhibit the anisotropic patterns expected in ${\mathrm{O}}_{\mathit{h}}$ symmetry. Calculations of two-photon transition intensities are conducted within the framework of the phenomenological model previously used for ${\mathrm{Sm}}^{2+}$ in MClF (M=Ba,Sr) and ${\mathrm{Eu}}^{3+}$ in ${\mathrm{LuPO}}_4$, where the rare-earth ion occupies sites of ${\mathit{C}}_{4\mathit{v}}$ and ${\mathit{D}}_{2\mathit{d}}$ symmetries, respectively. The present results are compared and contrasted with those obtained in these previous cases.

• Received 14 September 1992

DOI:https://doi.org/10.1103/PhysRevB.47.11712