RAMAN-SCATTERING OF CHROMIUM-DOPED HALIDE ELPASOLITE CRYSTALS

Polarized Raman spectra of a single crystal of the chromium-doped elpasolite K2NaScF6:Cr3+ yield an unambiguous identification of the symmetries and frequencies of the four Raman-active modes: a1g at 525 cm-1, e(g) at 403 cm-1 and t2g at 250 and 113 cm-1. Low temperature spectra reveal a lower symmetry phase involving substantial distortion of the potassium sublattice. The impurity concentration dependence reveals a local mode of a1g symmetry at 541 cm-1. Vibration frequencies inferred from unpolarized Raman spectra are reported for a number of other halide elpasolites doped with either chromium or titanium.