Variation of the absorption spectra and optical energy gap with γ-ray irradiation and heat treatment in SbNbO4 films deposited on MgO and quartz substrates

The effects of both γ-rays irradiation and annealing temperature on the optical absorption spectra of SbNbO4 films deposited on MgO or quartz substrates in the spectral range 190–800 nm were studied. The dose of γ-ray irradiation was varied up to 100 kGy and the annealing temperature was varied up to 900 °C. The transmittance and the reflectance were measured and hence the absorption coefficient was estimated. Annealing and γ-rays irradiation changed the general level of absorption in the treated films. A number of bands show a continuous shift in position and decrease in intensity with increasing γ-dose. The allowed optical transitions were found to be indirect transitions, hence values of the allowed indirect optical energy gap was calculated as a function of γ-dose and heat annealing temperature. The results can be discussed on the basis of γ-irradiation-induced defects in the film and on the film microstructure. The optical parameters of SbNbO4 films are affected by the kind of substrate. The effect is more pronounced in case of films deposited on quartz substrates.