Optical investigation of electron-beam-deposited tungsten-tellurite (TeO2)100-x(WO3)x amorphous films

Amorphous films of (100 - x)TeO2-xWO3 with compositions 7.5 epsilon x 40 mol. % were prepared by electron-beam evaporation. The compositional dependence of the optical properties of the prepared films was analyzed by the Swanepoel envelope method, which revealed that the refractive index increases with increasing tungsten oxide content. The Wemple-DiDomenico dispersion model was used to explain the refractive index increase in terms of the formation of W-O-Te bonds, which have a higher energy than that of Te-O-Te bonds. A fitting of the spectral dependence of the absorption coefficient to the Tauc relation allowed a determination of the optical band gap, [image omitted], which is found to decrease linearly with increasing tungsten oxide percentage.