The 3-dimensional thermoluminescence spectra of single crystals which had been grown from the melt by using the Czochralski technique, or pulled from a flux using the top-seeded solution growth method, were studied after irradiation. The thermoluminescence spectra were recorded for wavelengths ranging from 200 to 800nm, and temperatures ranging from 20 to 300K, before and after annealing in an O atmosphere. It was found that, in spite of the differing growth conditions, the 3-dimensional thermoluminescence spectra of the Czochralski samples exhibited similar thermoluminescence characteristics. The main thermoluminescence emission appeared around 450nm, at between 200 and 250K. Further weak emissions were also detected at 570, 600, 650, and 710nm. These were tentatively attributed to impurities. The thermoluminescence spectrum of the top-seeded solution grown crystal differed markedly from that of the Czochralski crystals. The major thermoluminescence peak appeared at lower temperatures here, whereas the emission spectrum exhibited a broader band around 500nm and the weak bands between 500 and 700nm could not be detected. It was concluded that heat treatments, such as annealing in an O atmosphere, could modify the defect structures in 2 ways. Firstly, they could compensate O vacancies and, secondly, they could produce additional precipitation due to a limited solubility region in the quasi-congruent composition. Precipitates in the form of an Y or V excess further increased the defect content on anion and/or cation sites in near-congruent crystals. Annealing in O increased most of the thermoluminescence peak intensities (except for peaks at 210 and 241K). It was assumed that the corresponding traps represented both cation and anion site defects.

S.Erdei, L.Kovács, A.Peto, J.Vandlik, P.D.Townsend, F.W.Ainger: Journal of Applied Physics, 1997, 82[5], 2567-71