The two photorefractive centres in iron doped nearly stoichiometric lithium niobate crystals

This paper investigates the photorefractive properties of iron doped lithium niobate with different Li/Nb ratios. The experimental results show two photorefractive centres for iron doped near-stoichiometric lithium niobate crystal. Besides Fe^2 + and Fe^3 + ions, small polarons and bipolarons are considered as another photoactive centre.