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We grew a set of indium and molybdenum co-doped lithium niobate crystals with various indium doping concentrations and investigated their photorefractive properties at different wavelengths (442, 488 and 532 nm). It was found that the diffraction efficiency of 1.0 mol% indium and 0.5 mol% molybdenum co-doped lithium niobate crystal could reach 61.57% at 488 nm. Moreover for 3.0 mol% indium and 0.5 mol% molybdenum co-doped lithium niobate crystal, the response time was greatly shortened to 0.61, 0.76, and 0.74 s at 442, 488, and 532 nm, respectively, while the photorefractive sensitivity reached as high as 7.35 cm/J at 442 nm. These results indicate that co-doping of indium is an efficient way to further enhance the photorefractive properties of molybdenum-doped lithium niobate crystal.We grew a set of indium and molybdenum co-doped lithium niobate crystals with various indium doping concentrations and investigated their photorefractive properties at different wavelengths (442, 488 and 532 nm). It was found that the diffraction efficiency of 1.0 mol% indium and 0.5 mol% molybdenum co-doped lithium niobate crystal could reach 61.57% at 488 nm. Moreover for 3.0 mol% indium and 0.5 mol% molybdenum co-doped lithium niobate crystal, the response time was greatly shortened to 0.61, 0.76, and 0.74 s at 442, 488, and 532 nm, respectively, while the photorefractive sensitivity reached as high as 7.35 cm/J at 442 nm. These results indicate that co-doping of indium is an efficient way to further enhance the photorefractive properties of molybdenum-doped lithium niobate crystal.

Bismuth-doped lithium niobate (LN:Bi) crystals were grown by Czochralski method and their optical damage resistance, photorefraction, absorption spectra, and defect energy levels were investigated. The experimental results indicate that the photorefractive properties of LN:Bi were enhanced as compared with congruent one, the photorefractive response time was greatly shortened, the photorefractive sensitivity was increased, and the diffraction efficiency of near-stoichiometric LN:Bi (SLN:Bi) reached 31.72% and 49.08% at 532 nm and 488 nm laser, respectively (light intensity of 400 mW/cm2). An absorption peak at about 350 nm was observed in the absorption spectrum of LN:Bi. And the defect energy levels simulation indicates new defect levels appear in the forbidden gap of LN:Bi crystals. Therefore bismuth can act as photorefractive centers in LN crystals.

Till now it is difficult to obtain a p-type lithium niobate crystal. Here the carrier types in various doped and oxidized LiNbO3 crystals have been investigated by holographic technique. The experimental results show tetravalent ions (Zr4+ and Hf4+) with doping concentrations just above optical damage resistant thresholds is helpful to increase the concentration of holes. And 3.0 mol% ZrO2 doped LiNbO3 can be used as a p-type crystal. The dominant carrier of iron doped LiNbO3 crystal can be changed to holes when treated by thermo-electric oxidization. Then the possible mechanism on how to obtain a p-type LiNbO3 was discussed.