Laser Raman and far-infrared spectra of Gd 2(MoO 4) 3, Tb 2(MoO 4) 3, GdTb(MoO 4) 3, GdDY(MoO 4) 3, Tb 1.8Eu 0.2(MoO 4) 3 and Gd 0.2Dy 0.9Tb 0.9(MoO 4) 3 single crystals in the external mode region

Abstract

Laser Raman and Fourier transform far-infrared (FT-FIR) spectra of rare earth molybdate single crystals of Gd 2(MoO 4) 3, Tb 2(MoO 4) 3, GdTb(MoO 4) 3, GdDy(MoO 4) 3, Tb 1.8Eu 0.2(MoO 4) 3 and Gd 0.2Dy 0.9Tb 0.9(MoO 4) 3 were recorded. Based on C 2ν symmetry, group theoretical analysis was carried out and a vibrational assignment is proposed for the lattice modes of the rare earth and molybdate ions. For the first time bands are observed in the region 10–40 cm −1 in FT-FIR spectra and they are assigned as difference bands. LO-TO splittings in these noncentrosymmetric systems are also discussed.