A study was made of the electric charge and defect accumulation that was produced, by X-irradiation at 80K and 290K or 3keV electron irradiation at 290K, in nominally pure -phase crystals which had been grown under various reducing conditions. Subsequent thermally stimulated relaxation electronic and ionic processes were investigated, at 80 to 700K, by using thermally stimulated current, depolarization current, luminescence, electron emission, ionic thermocurrent and X-ray excited luminescence spectroscopic techniques. It was found that defect, charge and energy accumulation in non-reduced samples under X-irradiation was caused mainly by electron and hole capture at pre-irradiation defects. The main luminescence peaks, at about 110K, 160K, 250K, 280K, 360 to 380K, 460 to 480K and 520 to 550K were associated with correlated strong thermally stimulated current, depolarization current and electron emission peaks. A predominance of the electron transfer (c-band) component in many thermally stimulated relaxation phenomena (electrical conductivity, polarization -depolarization, electron radiative or non-radiative recombination, electron emission) was observed at 80 to 700K. In the case of reduced crystals, two dipolar defects were detected which produced ionic thermocurrent peaks at about 250 and 590K. The first was tentatively attributed to OH- and/or F--centers, and the second to an anion vacancy.

V.Ziraps, V.Graveris, I.Kruminš: Materials Science Forum, 1997, 239-241, 69-72