Effect of X-ray radiation on the optical properties of photorefractive bismuth-silicate crystals

The results of investigations of the optical-absorption spectra of bismuth-silicate (Bi$_{12}$SiO$_{20}$) single crystals are presented. The band-gap width and the characteristic Urbach energy are determined. The effect of preliminary X-ray irradiation on the behavior of the experimental spectral dependences and the values of the characteristic parameters induced by the bismuth-silicate defect structure is established.