Luminescence of Sm2+ ions as a probe of pressure-induced phase transitions in SrF2.

Abstract

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