Radiation-induced electrical and optical processes in materials based on Al2O3

The irradiation of dielectrics induces electric charging of microscopic reg ions in the bulk, which is associated with concentration inhomogeneities in the system of traps and the differences in characteristic diffusion length s of free electrons and holes that are produced in ion tracks and collision cascades. Experimental data on radiation-induced luminescence (RIL) give e vidence of the existence of three states of oxygen vacancies in Al2O3: an o ptically inactive (electrically neutral) vacancy, its excited state (known as F+ center), and a negatively charged vacancy (F center). The formation o f negatively charged regions under irradiation increases the intensity of t he 415-nm band of F centers of RIL of Al2O3 Single crystals. In Al2O3:Cr3ceramics, a radiation-induced negative charging of grain boundaries with re spect to the bulk of grains takes place, which manifests itself as an incre ase in the intensity of the 690-nm band of RIL of Cr3+ ions, whereas the in tensity of this band in Al2O3:Cr3+ single crystals remains unchanged. Using data on RIL, the local-charge density in grains of Al2O3:Cr3+ ceramics and the field produced by this charge are estimated. (C) 2001 MAIK "Nauka/Inte rperiodica".