ABSTRACT
This chapter considers mainly photoinduced transfer of charge and optical phenomena in glasses and microcrystals distributed in vitreous dielectric hosts. So there emerges a need for a brief and uniform description of the basic information on the spectroscopic characteristics and photochemical processes in solids. For a long time photoinduced processes in different materials were a subject of thorough investigation by researchers working in many branches of science. The photochromic process, the reversible variation of an absorption spectrum under optical irradiation, is usually due to the fact that the electron subsystem of solids absorbs photons. The absorption due to electron transitions in a defect-free substance of stoichiometric composition is called intrinsic, basic, or fundamental absorption. To shift the range of photochromism excitation to long wavelengths, it is necessary to use dopants in their lowest valence state that can be ionized by near UV irradiation.
