Electron paramagnetic resonance methods were used to identify the primary electron and hole traps which were responsible for so-called gray tracks in flux-grown samples. Ionizing radiation in the form of X-rays was used to produce the gray-track effect. During irradiation at 0C, a broad absorption band which peaked at 500nm was introduced. Also, electron paramagnetic resonance spectra from a series of Ti3+ centers appeared, and the predominant electron paramagnetic resonance spectrum (which was associated with Fe3+ ions) decreased significantly. Following irradiation, the decay of the optical absorption and the Ti3+ centers - together with the growth of Fe3+ centers - was monitored for 20h at room temperature. Changes in the electron paramagnetic resonance spectra of the Ti3+ and Fe3+ centers during annealing was correlated with the decay of the induced optical absorption (gray tracks). It was concluded that the Fe3+ centers were the primary hole traps and that Ti4+-Vo complexes were the primary electron traps which were responsible for gray track formation in flux-grown crystals.

M.P.Scripsick, D.N.Lolacono, J.Rottenberg, S.H.Goellner, L.E.Halliburton, F.K.Hopkins: Applied Physics Letters, 1995, 66[25], 3428-30