Instability of photoinduced optical absorption of Bi$_{12}$SiO$_{20}$: Al crystals

The results of the experimental investigation of the instability of the establishment and relaxation of a photochromic effect in aluminum-doped Bi$_{12}$SiO$_{20}$ crystals have been presented. The oscillating and nonmonotonic kinetic dependences of the photoinduced optical absorption have been observed. The absorption oscillations are associated with the competition of the formation and destruction of [Al$_{\mathrm{Si}}$O$_4$]$^0$ photochromic centers.