Optical Properties and Structure of As-Sb Chalcohalide Glasses by Raman Scattering and Density Functional Theory Calculations.

We report an investigation of the optical properties, structure, and vibrational modes of SbxAs37-xS48I15 glasses (0 at. % < x < 37 at. %). Optical parameters such as the refractive index, the absorption coefficient, and the optical band gap are correlated with the glass composition. All parameters were found to follow an almost linear dependence with the antimony content x. Both the refractive index and the absorption edge wavelength exhibit a systematic increase against x. Off-resonant Raman spectra of the glasses spectra were measured and analyzed. Structural units, representative of the glass structure, were optimized by density functional theory (DFT) calculations, providing vibrational spectra in agreement with the experiments. Raman spectra were interpreted based on the harmonic frequencies and the activities of vibrational modes obtained by the DFT analysis. The results showed evidence in favor of statistical mixing of iodine atoms, among the various pyramidal units, hence discarding structural models suggesting the presence of isolated pyramidal molecules of the types AsI3/SbI3. Both experimental data and DFT results suggested that iodine atoms exhibit much higher propensity to replace sulfur atoms in antimony than in arsenic-based pyramids. In addition, comparison of experimental and simulated spectra of selected clusters in mixed glasses indicates that it is more probable to find corner-sharing Sb-based pyramids than As-based ones.