Lattice dynamics and optical properties of yttrium oxysulfide

Lattice dynamics and optical properties of yttrium oxysulfide have been investigated with the combination of microscopic Raman scattering experiment and first-principles calculation. The Raman scattering experiment on our single crystals ensures an earlier Raman spectrum based on powdered samples. Ab initio calculation based on density-functional perturbation theory is performed to obtain the phonon modes in the first Brillouin zone, dielectric and Born effective charge tensors in the uniaxial crystal structure. A rigorous assignment of all the phonon modes at Γ-point is achieved, in agreement with the previous and present Raman experimental data. The calculated results also indicate the ambiguity of infra-red experimental results on oxysulfides. Since these physical values are related to the properties of polaron, our theoretical approach may be useful to understand optoelectronic processes such as scintillation.