Single-oscillator description of spectral dependence of the refractive index of new chalcogenide Ge-Sb-(S,Te) glasses

New quaternary telluride glasses based on Ge-S system with addition of Sb and partial substitution of S by Te have been synthesized and their optical properties in dependence on composition have been studied by spectroscopic ellipsometry in 400-820 nm spectral range. The dispersion behavior of the refractive index of these glasses with composition of GexSb40-xS50Te10 and GexSb40-xS55Te5 (x= 10, 20, and 27) was examined applying the single-oscillator theory and using the Wempel-DiDomenico's model. From the data analysis the optical constants (n, k, ε), optical bandgap energy Eog and film thickness, as well as the oscillator energies E0 and Ed have been determined. The observed increase of E0 and decrease of Ed with increasing the Ge content or decreasing the Te content are explained by the change of amount and strength of heteropolar chemical bonds and by the less covalent character of chemical bonding in these materials. Correlation between the oscillator energy E0 and optical band gap energy Eog is established.