Spectral dependence of photorefractive erasure in Bi12GeO20 and Bi12SiO20

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Abstract
A holographic method similar to that previously used with LiNbO3 to study the spectral behavior of photorefractive centers has been applied to Bi12SiO20 (BSO) and Bi12GeO20 (BGO). By erasing with incoherent light a previously written grating, measurements of the grating decay constants as a function of the erasing wavelength have been carried out. The grating erasure exhibits decays made up of a sum of two exponential terms for all wavelengths between 390 and 620 nm. In terms of recent photorefractive models which use two active species, our results imply that there exist two different photorefractive centers in BGO and BSO. By numerically fitting the observed spectral dependencies of the decay constants to the model equations, the absorption bands associated to these centers have been obtained. Their peak positions and half‐widths are the following: 2.7 eV (0.27 eV) and 3.1 eV (0.4 eV) for BSO; 2.8 eV (0.3 eV) and 3.1 eV (0.4 eV) for BGO.