Study Of Growth And Photorefractive Anisotropy Of Fe-Mn Codoped Lithium Niobate Crystal

In this paper, different diameters of congruent lithium niobate crystals where the Li/Nb ratios showed to be 0.946, content of Fe revealed 0.075 mass% and the proportion of Mn was 0.012mass% which were treated as oxidization and reduction. The intrinsic defect, location of doped ions and holographic storage properties of the crystals were investigated in common cut ways as well as 45 angle cut.The results showed that all the Fe:Mn:LiNbO₃ crystals hold the same lattice structures as the pure congruent LiNbO₃. It demonstrated that the doping ions enter lattice by the replacement of Li or Nb ions. The lattice constants increased compared with pure LiNbO₃. Using infrared spectra and absorption spectra, the location of Fe and Mn irons in the crystals were confirmed, and the location model can be explained like that both the Fe and Mn irons occupied the normal Li sites where appeared defects Fe_Li²⁺ of Fe_Li⁺ , Mn(Li)²⁺ and Mn(Li)³⁺ ,and the vacancy Li compensated for the lost electric charge. For the polarized ability of Feand Mn²⁺/Mn³⁺ were both superior to Li⁺, which induced the increase of O^2- polarization, the electron cloud turned to be distorted and enlarged, the needed energy for electron transition would decrease. Thus, the absorption edge appeared to be shifted to the red. The results of the test of Curie temperature indicated that the Curie temperature decreased with the volatilization of Li while there is no evidence to show linear relation between the two.The holographic storage properties including diffraction efficiency, response time, erase time and so on in different cut ways have been tested. The result indicates that the holographic storage properties of the crystals were affected by different cut ways and treated conditions of crystals. Wafer cutted as frequency angle 45 showed that the diffraction efficiency and response time decreased, the dynamic range and the photorefractive sensitivity were enhanced. While the c axis cut ways indicated that the diffraction efficiency and response time increased compared to 45 angle cut wafers. The dynamic range and the photorefractive sensitivity reduced The diffraction efficiency increased but the response and erase time become longer in oxidized crystal and that is reversed in the reduced crystal.The holographic storage properties of LiNbO₃ crystal could be adjust by proper cut way as well as the treated ways. The LiNbO₃ crystal with excellent holographic storage properties would be gained by these methods.