Study On Growth And Photorefractive Properties Of Lithium Niobate Doped With Magnesium And Iron

Series of Mg:Fe:LiNbO₃ crystals were grown by the Czochralski method. The growth and structure and the optical properties of the crystals were studied. Appropriate parameters (temperature gradient, pulling speed and rotating speed) are chosen during the crystal growth process to maintain the flat solid-liquid interface.O-H absorption peak of Mg(6mol%):Fe:LiNbO₃ crystal shifts to 3535cm^-1 compared with that of other crystals doped with lower Mg concentration 3482cm-1,which indicates that Mg doping concentration of 6mol% is over the threshold. With the increase of Mg doping amount,the absorption edge in ultraviolet-visible absorption spectra of Mg:Fe:LiNbO₃ crystal shifts to the violet. Using infrared spectra and absorption spectra, the location of Mg in doped LiNbO₃ crystals were confirmed, and the location model was given. Before the doped concentration of Mg achieves its threshold Mg takes anti-site Nb(NbLi),and when the doped concentration of Mg over its threshold, Mg enters NbNb and LiLi sites at the same time.The holographic storage properties including diffraction efficiency, response time, erase time and photo damage resistance ability were measured. We found that the holographic storage properties of the Mg:Fe:LiNbO₃ crystals were affected by the Li/Nb ratio and the treating state of crystals. The results show that the diffraction efficiency and response time decreased and the photo damage resistance ability is enhanced with the increasing of Li/Nb ratio.The holographic storage properties of LiNbO₃ crystal could be adjust by doping impurities and changing Li/Nb ratio. The LiNbO₃ crystal with excellent holographic storage properties would be gained by these methods.