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

Concentration inhomogeneities in the trap system have been shown to be resp onsible for radiation-induced electric charging of regions in the bulk of d ielectrics under irradiation. Formation of electrically charged regions is caused by difference in hopping mobility of charge carriers over traps and does not violate general electric neutrality of the system. Formation of ne gatively charged regions during irradiation results in intensity increase f or F-centres band (415 nm) in radiation-induced luminescence (RIL) spectra of single crystal Al2O3. In ceramic Al2O3:Cr3+, the radiation;induced negat ive charging of grain boundaries with respect to grain bulk takes place whi ch is revealed in the intensity increase of Cr3+ ion RIL band (690 nm), in spite of a constant intensity of this band in single crystal Al2O3:Cr3+ und er similar conditions. The idea of the radiation-induced electric charging due to concentration inhomogeneities in the trap system allows one, using t he RIL method, estimating local charge density in grains of ceramic Al2O3:C r3+ and associated electric field. Under 8 MeV proton irradiation (dose rat e up to 5 x 10(3) Gy/s), excessive positive charge in grains of ceramic Al2 O3:Cr3+ exceeds 10(4) Q/m(3), and associated electric field exceeds 10(6) V /m. (C) 1999 Elsevier Science B.V. All rights reserved.