Laser-induced fluorescence line narrowing inSm2+-doped fluoride glass

Fluorescence line-narrowing experiments have been made for the ${\mathrm{Sm}}^{2+}$ ion in fluoride glass at 77 K under cw dye-laser excitation at various energies within the inhomogeneously broadened ${}_{}{}^7{}_{}{}^{}$ ${\mathit{F}}_{0\mathrm{-}}^5$ ${\mathit{D}}_0$ and ${}_{}{}^7{}_{}{}^{}$ ${\mathit{F}}_{0\mathrm{-}}^5$ ${\mathit{D}}_1$ absorption lines. The energies of the three Stark levels of the ${}_{}{}^7{}_{}{}^{}$ ${\mathit{F}}_1$ and ${}_{}{}^5{}_{}{}^{}$ ${\mathit{D}}_1$ manifolds have been obtained as a function of the ${}_{}{}^5{}_{}{}^{}$ ${\mathit{D}}_{0\mathrm{-}}^7$ ${\mathit{F}}_0$ energy separation. From the analysis of this result, it has been found that the site-to-site variations of the energies of these Stark levels can be explained well only by taking into account the J-mixing effect. The low-energy levels of the 4${\mathit{f}}^5$5d configuration lie in the vicinity of the ${}_{}{}^5{}_{}{}^{}$ ${\mathit{D}}_{\mathit{J}}$ states in this material. However, no effect of the crystal-field mixing of the 4${\mathit{f}}^5$5d states on the inhomogeneous distribution of the energies of the ${}_{}{}^7{}_{}{}^{}$ ${\mathit{F}}_1$ and ${}_{}{}^5{}_{}{}^{}$ ${\mathit{D}}_1$ states has been observed. The origin of the unusually intense ${}_{}{}^5{}_{}{}^{}$ ${\mathit{D}}_{0\mathrm{-}}^7$ ${\mathit{F}}_0$ transition in ${\mathrm{Sm}}^{2+}$ is also discussed.