ABSTRACT
The stimulation of photochromic glasses by visible radiation was reported that under certain conditions an increase in photoinduced absorption is caused by that radiation. Several possible mechanisms can be offered for the explanation of long wavelength stimulation of coloration. In the work by Ashkalunin et al., which was the first description of the phenomenon, it was assumed, that under long wavelength excitation, the ionization of previously created color centers occurs. Coloration produced by photons with energy that is not enough for photosensitivity center ionization and the dependence of the long wavelength stimulation efficiency on radiation intensity can lead to the assumption of two-photon ionization of photosensitive centers. To explain all features of the long wavelength coloration of photochromic glasses attention can be drawn to another type of nonlinear process observed by Ovsyankin et al. in silver halide crystals, namely, the cooperative sensitization of luminescence.
