Stability and Optical Properties of gamma-Gd2S3 at High Pressures

High pressure behavior of gamma-Gd2S3 (I 3d, Z=4) is studied with X-ray diffraction, Raman spectroscopy, and optical reflectivity. Upon compression to 30 GPa there is no structural phase transition. The pressure dependence of the infrared transparency in this material to 30 GPa is determined from its bulk modulus, extracted from the X-ray data, and the pressure shift of the highest wavenumber first-order Raman mode. Optical reflectivity spectra up to 20 GPa show a red shift of the lowest energy direct interband transitions. At higher pressures, broadening of the reflectivity spectral features is associated with a loss of Raman intensity as a result of a possible transformation in the electronic structure. Free carriers do not emerge up to 35 GPa, indicating that gamma-Gd2S3 remains semiconducting.