Abstract

The spectroscopy of several centres in Bi₁₂SiO₂₀ which are related to its photorefractive behaviour will be presented and discussed. In a recent paper, the spectral dependence of the photorefractive erasure by using the holographic method has been studied [1]. Two major absorption bands producing photorefractive erasure were found, their peak positions and halfwidths respectively being 2.7 eV (0.27 eV) and 3.1 eV (0.4 eV). These bands were obtained by numerically fitting the experimental decay constants for each erasing wavelength to those predicted by a two centre model [2] in which fast carrier exchange between the two traps was assumed. Because of practical reasons related with the fitting process, the geometrical shadow effect (sample selfabsorption) was not taken into account in that paper. Therefore the band parameters obtained from photorefractive erasure are necessarily a first approximation which should be improved with other measurements. In this paper, an analysis of the optical absorption and photoconductivity spectra based in those gaussian components is presented. This analysis is expected to provide a more detailed knowledge of the bands responsible for the optical absorption, photoconductivity and photorefractiorn, although the actual nature of the centres originating the bands remains uncertain. Photochromic effects induced on these bands by low temperature illumination, as well as their thermal annealing, will be also considered.

© 1990 Optical Society of America