Infrared-spectroscopic study of orthorhombic YF3 and LuF3 single crystals

Polarized infrared-reflectivity spectra have been obtained for Czochralski-grown YF3 and LuF3 single crystals, at room temperature. At this temperature these crystals exhibit an orthorhombic symmetry belonging to the Pnma (D2h16) space group, known as β-YF3. The measured spectra were analyzed based on the factor-group method and on the fitting with the four-parameter semi-quantum model. The observed modes obey well the selection rules and the 16 predicted infrared-active modes could be depicted and assigned to their corresponding symmetries for both crystals. From the frequency splitting of TOLO modes, the ionic effective charges were calculated and the results used to discuss the potentiality of laser action of β-YF3-type crystals.