Oxygen ion-induced modifications of optical properties of natural muscovite mica

Abstract

Optical modifications of natural muscovite mica were investigated by irradiation of 80 MeV O6+ ion beam at various fluences ranging from 5×1012 to 5×1013 ions/cm2. The optical absorption spectra in the wavelength range of 200–700 nm were recorded for the pristine and ion-irradiated samples in the above fluences to determine the values of the optical band gap (E g), and Urbach energy (E u). The width of the tail of localised states in the band gap (E u) was evaluated using the Urbach edge method. Both the indirect and direct band gaps in pristine and oxygen ion-irradiated natural muscovite mica have been studied, it was interesting to note that the values of indirect band gap were found to be lower than the corresponding values of the direct band gap. A shift in the absorbance edge towards longer wavelength region appeared in the UV–VIS spectra with increasing ion fluence which indicates that the optical energy band gap is decreasing. This influence of ion irradiation on the optical gap was explained in terms of diminution of disorder and defects in the structural bonding of samples.