Radiative transitions in crystals of sillenite-type structure

The complicated spectrum of radiative transitions in sillenite-type crystals is investigated. It is shown that the luminescence excitation spectra (LES) of crystals studied can be divided into three groups: a) the excitation in the fundamental absorption band leading to a generation of electron–hole pairs (330 nm); b) exciton excitation resulting in their autolocalization (370 nm); c) activation excitation leading to a generation of free electrons (470 and 640 nm). The temperature dependences of the photoluminescence (PL) intensity are investigated and the activation energies are determined. The irradiation by electrons and thermal annealing in vacuum are shown to result in an interrelated change of PL and luminescence excitation spectra. A new (red) band of PL (1040 nm) attributed to oxygen vacancies in the crystals considered is found. The PL kinetics at excitation of sillenites by nanosecond pulses is studied. It is shown that the PL is quenched exponentially with temperature and the values of the PL quenching constants are determined.