Excitation and erasure of photochromic effect in the Bi12SiO20 crystals doped with Al, Ga and Sn

We present the results of experimental investigations of the processes of excitation and erasure of photochromic effect (PCE) in undoped Bi12SiO20 (BSO) crystals and the BSO crystals doped with Al, Ga and Sn ions (BSO:Al, BSO:Ga and BSO:Sn, respectively). The PCE spectra, the spectra of optical erasure of the PCE (OE PCE), as well as the PCE excitation and PCE erasure functions are obtained. It is demonstrated that the sets of individual components of the PCE spectra for the doped crystals are very similar for different impurity ions, though the intensities of those components are different. Doping of BSO manifests itself in weakening PCE in the blue-green region of the spectrum and its strengthening in the spectral region given by h nu = 0.5 divided by 2.0 eV. The OE PCE is almost complete and the components that cannot be erased are observed only for the BSO: Sn crystals. We have evidenced that a limiting photon energy (h nu* approximate to 2 eV) exists, for which the photoexcitation leads to the PCE for the crystals staying in their initial stationary state, but erases the PCE if the crystals passed into the state with the maximal saturated PCE.