Radiation effects and defects in lithium borate crystals

Abstract

The paper presents the results of a study of the formation and decay of lattice defects in wide band-gap optical crystals of LiB 3O 5 (LBO), Li 2B 4O 7 (LTB) and Li 6Gd(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. © 2010 IOP Publishing Ltd.