Study On Defect Structure And Photorefractive Properties Of Lithium Niobate Doped With Ruthenium And Iron

The optical holographic storage is the promising storage technique because of its high storage density, high transfer speed, fast parallel access, and so on. Lithium Niobate (LiNbO₃) crystal has become one important holographic storage materials contributed by its well-known photorefractive performance, such as high diffraction efficiency, high storage density and long storage lifetime. However, LiNbO₃ crystal exhibits the relatively low response speed, strong light-induced scattering and volatility, which limits the holographic storage. So, improving and optimizing the photorefractive performance of LiNbO₃ crystals attract more attention and become an important research subject in recent years. In this thesis, the Ru, Fe co-doped LiNbO₃ crystals were grown by Czochralski method, and the crystals have no macroscopic defect and have good optical homogeneity. The intrinsic defects, location of doped ions and photorefractive properties of the Ru: Fe: LiNbO₃ crystals.The defect structure and occupied sites of Ru:Fe:LiNbO₃ crystals were investigated in detail by using infrared OH- absorption spectra, UV-Visible absorption spectra, and the X-ray analysis. The results of X-ray showed that all the Ru:Fe: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 Ru irons in the crystals were confirmed, and the location model can be explained like that both the Fe and Ru irons occupied the normal Li sites where appeared defects of FeLi²⁺(FeLi⁺) and RuLi³⁺(RuLi²⁺) and the vacancy Li compensated for the lost electric charge. For the polarized ability of Fe³⁺/Fe²⁺ and Ru⁴⁺/Ru³⁺ 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 red. Oxidation treatment only changed the absorbed extent of OH-absorption peaks, absorption peaks have not changed, nor appear the new absorption peaks. At the same time the absorption edges appeared to be shifted to purple.The photorefractive properties including diffraction efficiency, response time, erase time dynamic range, sensitivity and so on in different contents of Ru have been tested. The result indicates that the photorefractive properties of the crystals were affected by different contents of Ru and treated conditions of crystals. As the concentration of Ru increased, the diffraction efficiency increased, the response time decreased, the dynamic range and the photorefractive sensitivity were enhanced. While the treatment of oxidized indicated that the diffraction efficiency and response time increased compared to growth state. The dynamic range and the photorefractive sensitivity reduced. We also found that record and read out time of Ru:Fe:LiNbO₃ are serious asymmetry, reflects that the Ru:Fe:LiNbO₃ crystals have quasi-state non-volatile characteristics.This is also the first time to use dual-wavelength nonvolatile memory technologies to study nonvolatile photorefractive properties of Ru:Fe:LiNbO₃ crystals. Comparing to the conventional two-color nonvolatile recording, the dual-wavelength nonvolatile photorefractive properties are improved greatly.