The paper presents the results of a study of the formation and decay of lattice defects in wide band-gap optical crystals of LiB 3 O 5 (LBO), Li 2 B 4 O 7 (LTB) and Li 6 Gd(BO 3 ) 3 (LGBO) with a sublattice of mobile lithium cations. By means of thermoluminescence techniques, and luminescent and absorption optical spectroscopy with a nanosecond time resolution under excitation with an electron beam, it was revealed that the optical absorption in these crystals in the visible and ultraviolet spectral ranges is produced by optical hole-transitions from the local defect level to the valence band states. The valence band density of the states determines mainly the optical absorption spectral profile, and the relaxation kinetics is rated by the interdefect non-radiative tunnel recombination between the trapped-hole center and the Li 0 trapped-electron centers. At 290 K, the Li 0 centers are subject to thermally stimulated migration. Based on experimental results, the overall picture of thermally stimulated recombination processes with the participation of shallow traps was established for these crystals.

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The results of investigation of thermally stimulated recombination processes and luminescence in Li 6 Gd x Y 1-x (BO 3 ) 3 -Eu crystals are presented. The steady-state luminescence spectra under X-ray excitation (XRL), the temperature dependence of steady-state luminescence intensity and the thermally stimulated luminescence curves (TSL) were measured at 90-500 K. In the steady-state X-ray luminescence spectra the band at 312 nm related to 6 P J → 8 S 7/2 transitions in gadolinium ion and bands group at 580-700 nm associated with 5 D 0 → 7 F J transitions (J = 0…4) in Eu 3+ ion were found to be dominant. The intensity of steady-state XRL of these bands in undoped crystal is increased by 15 times as the temperature changes from 100 to 400 K. The probable mechanisms of temperature dependence of steadystate luminescence intensity and their association with energy transfer of electronic excitations in these crystals are discussed. The investigations have shown the principle complex TSL peak with maximum at 150 K and a number of weaker peaks. The thermal activation parameters (activation energy, pre-exponential factor, kinetic order) for all intense TSL peak have been determined. The origin of small trapping centres caused TSL below room temperature and their association with defects in lithium cation sublattice is discussed.