Spectroscopic properties of KGd(WO4)2: (Er, Yb) single crystals studied by Brillouin scattering method

Abstract The study of KGW: (Er, Yb) was performed for the acoustic phonons [1 0 0], [0 0 1], [−1 0 1], [1 0 1], [1 1 0] and [0 1 1]. In some Brillouin spectra obtained at room temperature we observed additional modes connected with mixed polarization modes propagating as quasi-longitudinal or quasi-transverse phonons which is characteristic for low symmetry crystals. Moreover, it has been revealed, that the value of Brillouin shift and integral intensity of the longitudinal phonon [1 0 1] propagating in KGW: (Er, Yb) show the anomaly at about 175 K.