Gated luminescence in as-grown and reduced undoped LiNbO3 crystals

The results of comparative study of the gated two-color luminescence and intrinsic optical absorption in as-grown and chemically reduced nominally pure LiNbO3 crystals are reported. A powerful laser beam at 514.5 nm was used as gating radiation, and a laser weak beam at 632.8 nm was used to probe the luminescence. The dependences of luminescence spectra on the power of gating radiation and crystal composition have been investigated. The luminescence intensity correlates with the bipolaron absorption band in the chemically reduced crystal. We conclude that this gated luminescence at 800-950 nm is caused by the radiative transitions involving polaron states and it may be directly correlated with the two-color photorefractive sensitivity used for gated holographic recording.