Optical properties of glasses (TeO 2–GeO 2–K 2O) thin films co-doped with rare earth oxides Sm 2O 3/Yb 2O 3

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Glassy thin films of [TeO 2–GeO 2–K 2O] co-doped with rare earth oxides Sm 2O 3/Yb 2O 3 were prepared by electron beam evaporation technique on polished fused silica glass substrate. The effect of Sm 2O 3/Yb 2O 3 rare earth sub-oxides co-doping on optical properties of glasses 80TeO 2–10GeO 2–8K 2O thin films has been investigated using optical spectrophotometry measurements in the wavelength range 200–2500 nm. The structural characteristics studied by X-ray diffraction (XRD) showed that all the films are amorphous. The fundamental optical parameters like band gap and absorption coefficient are calculated in the strong absorption region of transmittance and reflectance spectrum. The possible optical transition in these films is found to be allowed indirect transition with energy gap E g opt decreases from 1.27 to 1.06 eV with increasing Yb 2O 3 at expense of Sm 2O 3. The decreasing in E g opt can be interpreted in terms of the non-stoichiometry of the films. The refractive indices have been evaluated in term of envelope method suggested by Swanepoel in the transparent region. The refractive index, n, can be extrapolated by Cauchy dispersion relationship over the whole spectra range. It is observed that the refractive index, n increases with increasing Yb 2O 3 at expense of Sm 2O 3 which might be related to the changes in the compositions of TeO 2 and GeO 2 sub-oxides in the films.