Luminescence and transient optical absorption in CdWO4

Time-resolved luminescence and transient optical absorption of CdWO4 crystals were studied under electron beam excitation (270 keV, 10 nsec). Also the luminescence decay under laser pulse photoexcitation (337 nm, 10 nsec) was measured. At 300 K a wide emission band with a maximum at 2.45 eV was observed. With electron pulse excitation the luminescence decay in the spectral range of 2.0-2.85 eV consisted of two exponential components (2 mu sec and 11 mu sec). The decay of the photoluminescence shows single exponential decay with a time constant of 15 mu sec at 300 K. We conclude that under electron beam excitation (and gamma-ray excitation) an additional fast process is involved in CdWO4 emission. A wide nonsymmetrical transient optical absorption band, with a maximum at 2.5 eV is created under electron pulse irradiation. The relaxation of the transient absorption consists of two exponential components, with the same decay times as in luminescence. The induced absorption is due to the electron transitions from the radiative state of luminescence center to higher energy states. In our opinion, the short-lived process with a decay time of 2 mu sec, originates from the interaction of the excitonic radiative state with radiation-induced defects, created by the electron beam. This interaction leads to luminescence quenching and a fast decay of the induced optical absorption.