The luminescence of ${\mathrm{Sm}}^{2+}$ ions in ${\mathrm{SrF}}_2$ is used to monitor the β (cubic) -to-α (orthorhombic) phase transition of ${\mathrm{SrF}}_2$ at ∼5 GPa and 300 K. In contrast to those in the β phase, the ${\mathrm{Sm}}^{2+}$ spectra in the α phase show a series of sharp 4f-4f transition bands, even at 300 K, originating from the ${}_{}{}^5{}_{}{}^{}$${\mathit{D}}_0$ to ${}_{}{}^7{}_{}{}^{}$${\mathit{F}}_{\mathit{J}}$ multiplets including a strong transition for ΔJ=0. At low temperatures, these transitions are not observed; instead, the 4${\mathit{f}}^5$5${\mathit{d}}^1$ band of the ${\mathrm{Sm}}^{2+}$ ions in the β phase reversibly shifts below ${}_{}{}^5{}_{}{}^{}$${\mathit{D}}_0$ (4${\mathit{f}}^6$) level at 4.5 GPa and 30 K. The α phase is metastable and can be recovered at 1 atm and 30 K.

• Received 11 January 1991

DOI:https://doi.org/10.1103/PhysRevB.44.830