Photorefractive Properties And Structure Of Lithium Niobate Crystal Doped With Cerium

In this paper, a series of single doped lithium niobate single crystals and Ce/Mn codoped lithium niobate single crystals were grown from the melts with various Li/Nb ratios by Czochralski method. The high quality crystals were grown. The influence of growing conditions on the quality of crystals were studied, and the optium conditions for the crystal growth were used to grow the high quality crystals. After grown, crystals were poled, then cut along the specific direction. They can be used for testing after the skived and polished.The Li/Nb ratio, defect structure and the location of the dopant in the crystals were investigated by spectroscopy method. According to results of X-ray powder diffraction and Inductively Coupled Plasma-Atomic Emission Spectroscopy, the relationships between the exact composition and the raw materials, the Li/Nb ratio and the raw materials, the exact formula of the crystal, in the Ce:LiNbO₃ crystal and the Ce:Mn:LiNbO₃ crystal were determined. The exact composition formula of Ce:LiNbO₃ is Ce_mLi_nO_{1-n-(3m～4m)}NbO₃, in which m= 0.307+1.007x-0.369x² , n= -16.929+36.204x-16.647x² , x represents the [Li]/[Nb] in the melt. The exact composition formula of Ce:Mn:LiNbO₃ is Ce_mMn_nLi_oâ–¡_{1-o-(3m⁴m)-(2n³n)}NbO₃, in which m= 0.6771+0.32796x-0.06948x²,n= 10.73914-10.06163x+2.53387x² , o= -2.64856+5.46828x-1.43184x² , x represents the [Li]/[Nb] in the melt. The existing forms of the dopant in the crystal and the peaks in the laman spectral were also studied by theoretic analysis, differential thermal analysis, infrared spectra, ultraviolet-visible absorption spectra and laman spectra. The relationship between the FWHM and the Li/Nb ratio in the undoped crystal was modified for doped ones. The quantitative relation between the FWHM and the Li/Nb ratio of Ce:LiNbO₃ and Ce:Mn:LiNbO₃ are y - 1.14278 - 0.01845- E₁ (TO₁) and y - 1.14278 - 0.01845- E₁ (TO₁), respectively.The photo-refractive properties including diffraction efficiency, writing time, erase time were measured by two-coupled beam method, and the saturation value of the refractive-index change, photorefractive sensitivity and the dynamic range of crystals were calculated. The relation of the photorefractive properties and the crystal composition were studied. The results showed that the photo-refractive properties of the Ce:LiNbO₃ crystals are affected by the Li/Nb ratio and the treating state of crystals. The results showed that the diffraction efficiency increase, the photorefractive sensitivity and the dynamic range were enhanced with the increasing of Li/Nb ratio, but they will go to the opposite direction when the Li/Nb ratio reaches the certain value. Writing time decrease with the increase of Li/Nb ratio. The diffraction efficiency increase, photorefractive sensitivity and the dynamic range are enhanced. In the Ce:Mn:LiNbO₃ crystal, photorefractive sensitivity and the dynamic range of crystals were enhanced, but the diffraction efficiency, writing time and erase time were decreased with the increase of the Li/Nb ratio in the raw materials. The optical damage resistance ability of samples was scaled by the light spot distortion method. The result showed that the optical damage resistance ability of Ce:LiNbO₃ crystals and Ce:Mn:LiNbO₃ crystals were improved with the increase of the Li/Nb ratio in the melts. And the mechanism was also discussed in the paper. The holographic image storage and correlation recognition experiments were carried out in stiochiometric Ce:Mn:LiNbO₃ crystals which has the best integrate properties among the samples. It could be found that accuracy proportion of recognition was one hundred percent when 400 images were storaged in the crystal.The crystals with undoped stoichiometric lithium niobate crystal, undoped lithium niobate crystal with vacancy in the crystal, Ce doped lithium niobate crystal, Mn doped lithium niobate crystal and Ce/Mn co-doped lithium niobate crystals were investigated by First-principle mehtod. It includes the optimization of the crystal, the energy of the crystal, energy band of the crystal, density state and the optical properties of the crystals. The influence of the dopant on the energy band of the crystal, density state and the optical properties of the crystals were sutdied theoretically. According to the lowest energy principle and the comparation of crystal lattice after optimize and the change of refractive index to the experimental results, the form of defect structure was confirmed, the locations of the dopant in the crystal and the effect of the dopant on the structure and optic properties were also confirmed.