The time-resolved luminescence and transient optical absorption of crystals were studied during electron-beam excitation (270keV, 10ns), as was the luminescence decay under laser-pulse photo-excitation (337nm, 10ns). At 300K, a wide emission band with a maximum at 2.45eV was observed. Under electron-pulse excitation, the luminescence decay in the spectral range of 2.0 to 2.85eV consisted of 2 exponential components (2 and 11s). The decay of the photoluminescence exhibited a single exponential decay with a time constant of 15s at 300K. It was concluded that, under electron-beam excitation, an additional fast process was involved. A wide asymmetrical transient optical absorption band, with a maximum at 2.5eV, was created under electron-pulse irradiation. The relaxation of the transient absorption consisted of 2 exponential components; with the same decay times as in luminescence. The induced absorption was attributed to electron transitions, from the radiative state of the luminescence center, to higher energy states. It was suggested that the process with a decay time of 2s originated from the interaction of the excitonic radiative state with radiation-induced defects that were created by the electron beam. This interaction led to luminescence quenching and to a rapid decay of the induced optical absorption.

S.Chernov, R.Deych, L.Grigorjeva, D.Millers: Materials Science Forum, 1997, 239-241, 299-302