Light-induced Effects in Sillenite Crystals with Shallow and Deep Traps

This paper presents the light-induced effects in bismuth silicon and bismuth titanium oxide crystals associated both with the electron transitions into the conduction band and with the filling of shallow and deep traps, which determine the optical and electroconductive properties of these crystals. The dynamics of photoconductivity and light-induced absorption is analyzed under conditions of pulsed laser illumination at the wavelength of 532 nm. The possibility to describe the relaxation processes of a population for trapping levels with the use of two-exponential function is demonstrated. The photoconductivity dynamics is characterized by two relaxation times on the order of 100 ns and 10 μs, whereas for light-induced absorption the lifetimes about 10 μs and several days for short- and long-lived traps, respectively, have been obtained. Because of this, the relaxation transitions may be occurred both to the shallow trap centers with energy located close to the conduction band and to the deep-lying traps, which should be included into a diversified theoretical model adequately describing the light-induced phenomena in photorefractive sillenite-family crystals.