Study On Preparation, Structure And Photorefractive Properties Of Indium, Ferrum And Cuprum Co-doped Lithium Niobate Crystals

According to the theory of crystal growth and a mass of experiments exploration, the parameters for crystal growth were discussed and improved. On this basis, the appropriate technological conditions for growing doped LiNbO3 crystals were obtained. In accordance with the appropriate technological conditions, a series of Indium, Ferrum and Cuprum co-doped LiNbO3 crystals with regular exterior appearance and good optical homogeneity were grown by Czochraski method.The microstructure of the crystal samples were measured and analyzed by X-ray powders diffraction, infrared spectra, absorption spectra and DTA. The results show that there is no new phase appears in the LiNbO3 crystals, all these crystals are still LiNbO3 with trigonal system. The lattice constants of In:Fe:Cu:LiNbO3 crystals varied with the composition change. With the increasing of In ion concentration and Li/Nb ratio, the UV absorption edge shift to the violet and then to the red; the OH- absorption bands appear regular shifting. The locations of Cu, Fe and In ions in doped LiNbO3 crystals are confirmed. The effects of the In ion concentration and Li/Nb ratios on composition and micro-defect of In:Fe:Cu:LiNbO3 crystals were analyzed.It is determined that the doping threshold concentration of In ion in In:Fe:Cu:LiNbO3 crystal is 3mol%. With the In-doping concentration increasing, the location mode of In ion in crystal changed as following:firstly substitute anti-site Nb ions and normal Li ions;secondly normal Li ions; thirdly most normal Li ions and little Nb ions to form charge compensated defect complex. The photorefractive properties of In:Fe:Cu:LiNbO3 crystals are measured and studied systematically by two wave coupling experimental system. The results demonstrate that the photorefractive properties of In:Fe:Cu:LiNbO3 crystals are influenced by the Li/Nb ratio in crystal, the doping concentration of In ion and the state of oxidation or reduction. The diffraction efficiency and dynamic range decreases, the sensitivity increases and the writing time is shortened with the increasing of Li/Nb ratio or with the increasing of In ion doping concentration. From oxidation state to growth state to reduction state of the samples, the diffraction efficiency and the dynamic range decreases and the response time is shortened, but the sensitivity increases.The photodamage resistance ability of In:Fe:Cu:LiNbO3 crystals was measured by transmission facular distortion method. The results reveal that the photodamage resistance ability increase with the Li/Nb ratio and the In doping concentration increase. When the doping concentration of In ion exceeds 3mol%, the photodamage resistance ability of the crystals improves about two orders of magnitude higher than that of pure LiNbO3. The increase mechanism of photodamage resistance ability is discussed combining the location analysis of doping ions in LiNbO3 crystal.The nonvolatility storage performance of In:Fe:Cu:LiNbO3 crystals was measured. Using UV-light as gating light, He-Ne laser as recording light, two-photon fixing nonvolatile storage experimentation had been realized in In:Fe:Cu:LiNbO3 crystals. The results show, with the increasing of In ion doping concentration and Li/Nb ratio, the fixed diffraction efficiency decreased and writing time shortened. Among all the samples, In(1mol%):Fe:Cu:LiNbO3 and Fe:Cu:LiNbO3(Li/Nb=1.2) crystal show favorable nonvolatile properties for their large fixed diffraction efficiency and fast respond time.