Photorefraction in LiNbO₃ Crystals with Different Stoichiometry and/or Doped with Optical-Damage-Resistant Impurities

Summary

The photorefractive properties of LiNbO₃ with different [Li]/[Nb] ratios or/and doped with optical-damage-resistant impurities (ME = Mg, Zn, Sc, In, Hf, and Zr) are overviewed. The dependencies of the photorefraction on the composition caused mainly by variations in the photoconductivity are discussed in the framework of the two-center charge transport scheme. The origin of the photo-conductivity decrease is attributed to a variation in the shallow electron trap (Nb antisite) concentration or/and an alteration of Fe³⁺-like ion incorporation into the lattice, namely their partial localization on the Nb sites. An emphasis is given on an indubitable, although incomprehensible increase of the photovoltaic effect in Lienriched and ME-doped LiNbO₃. The photoinduced coloration (‘dark trace’ and GRIIRA effects) in LiNbO₃ is considered in terms of the contribution from intrinsic defects. An improvement of the photorefractive properties in LiNbO₃ at low ME doping is demonstrated and an appropriateness of these compositions for practical applications is examined.