Short-lived color and luminescence centers in LiNbO₃ crystals irradiated by pulsed electron beams

Data on spectra of short-lived optical absorption (SLOA) and luminescence induced in congruent crystals of lithium niobate by a pulsed electron beam (0.25 MeV, 20 ns, 15-160 mJ/cm²) in a temperature range of 80 to 350 K are presented. Anisotropic bands with maxima at 1.6 and 4.0 eV, originating from the capture of one and two conduction electrons by an (Nb_Nb-Nb_Li) complex, respectively, and weakly polarized bands at 2.5 and 3.3 eV due to holes located at Li and Nb vacancies are identified in the structure of SLOA spectra. Cathodoluminescence (CL) of lithium niobate crystals is characterized by fast (τ < 4 ns) decay and a broad spectrum, which contains the same bands as the SLOA spectra. It is shown that the change in the initial amount of defects in reduced crystals at 830 K results in an identical change in both the CL and SLOA spectra. A model which treats the luminescence as the result of radiative nonphonon transitions that accompany the thermalization of charge carriers captured into the ground state of a polaron is discussed.