【作者】 徐超；

【导师】 杨春晖；

【作者基本信息】 哈尔滨工业大学 ， 化学工程与技术， 2013， 博士

【摘要】 体全息存储由于具有高的存储密度、快速并行访问和快速传输速度等特点而被认为是新一代的存储技术。铌酸锂(LiNbO3，缩写LN)晶体是最重要的全息存储介质材料之一，它具有良好的光折变性能，如长的存储寿命和高的衍射效率等。但是，纯铌酸锂晶体存在响应速度慢、抗光致散射能力弱和读出过程的挥发性等问题，这些缺点限制了铌酸锂晶体的实际应用。近年来改进和优化铌酸锂晶体的全息存储性能具有越来越重要的意义。本论文中生长钌铁系列掺杂铌酸锂晶体并研究了晶体的结构和光学性能；根据光谱特性研究了钌铁系列铌酸锂晶体的缺陷结构；基于钌铁双光折变中心结构提出了光折变动力学方程，并详细分析了影响光折变效应的因素；最后采用双波长技术测试了晶体的非挥发全息存储性能。采用提拉法生长出了无宏观缺陷、光学均匀性良好的钌铁系列铌酸锂晶体。在晶体生长过程中，确定了最佳工艺参数(温度梯度、旋转速度和提拉速度)，保证了固液界面的平坦，减小了分凝造成的晶体成分的不均匀。通过X射线衍射谱、红外吸收光谱和紫外可见吸收光谱研究了钌铁系列铌酸锂晶体的缺陷结构和离子占位。ICP-AES测试结果表明锆离子的分凝系数在1附近变化。钌铁铌酸锂晶体和锆钌铁铌酸锂晶体的光学均匀性采用双折射梯度表征，结果显示随着锆掺杂晶体的光学均匀性下降。测试了晶体的OH-红外吸收光谱并采用洛伦兹方程拟合分析了锆离子的占位信息。和钌铁铌酸锂晶体相比，掺锆后吸收边向短波长方向移动，表明锆离子以取代反位铌的方式进入晶格。当晶体中锂数量增加，吸收边先蓝移后红移。当锆的掺杂浓度超过阈值时，锆离子同时占据锂位和铌位，形成Zr3+-Li-ZrN b缺陷保持电荷平衡，由此提出了离子取代模型。通过传统二波耦合实验研究了钌铁系列铌酸锂晶体的光折变性能。讨论了影响晶体光折变性能的因素如入射光波长、锆离子掺杂浓度、氧化还原处理和锂铌比等。结果显示钌铁铌酸锂晶体在蓝光下的衍射效率、响应时间、记录灵敏度和动态范围等均优于在红光下的数值。另外，在钌铁铌酸锂晶体中掺杂锆离子可以提高晶体的蓝光光折变性能。当晶体中锂铌比接近化学计量比时响应时间进一步缩短。由于锆离子掺杂和锂铌比提高使晶体中本征缺陷(反位铌和锂空位)数量减少使得性能参数的提高。采用透射光束光斑畸变和曝光能量流两种方法研究了钌铁系列铌酸锂晶体的抗光致散射性能。实验中系统研究了锆掺杂、氧化处理和锂铌比改变对晶体光致光散射的影响。结果显示生长态的钌铁铌酸锂晶体的光散射强于氧化态的晶体。锆掺杂和提高锂铌比可以有效抑制晶体中的光散射现象。分别使用双波长和双色技术研究了钌铁系列铌酸锂晶体的非挥发存储性能。载流子实验结果显示生长态钌铁铌酸锂和氧化态锆钌铁铌酸锂晶体在使用蓝光激光记录时的优势载流子是空穴，而用红光激光记录时优势载流子为电子。非挥发存储实验结果显示双波长存储技术能获得更强的存储性能，这是由于光栅直接记录、同相位特点以及晶体对蓝光更合适的光吸收。掺锆的钌铁铌酸锂晶体会获得更好的非挥发存储性能，表明锆钌铁铌酸锂晶体是优良的蓝光全息存储介质材料。更多还原

【Abstract】 The holographic volume storage is recognized as the next-generation storagetechnology due to its high storage density, fast parallel access and transfer speed.Lithium niobate （LiNbO₃, short for LN） crystal is believed to be one of the mostimportant holographic storage media because of its excellent photorefractiveproperties, such as long storage lifetime and high diffraction efficiency. However,slow response speed, weak light-induced scattering resistance and volatile duringreadout which exist in pure LiNbO₃crystal limit the practical application. Soimproving and optimizing the holographic properties of LiNbO₃crystal becomesmore and more significant in recent years. In this dissertation, a series of Ru and Fecodoped LiNbO₃crystals is grown and studied. The photorefractive kinetics formulawas proposed based on two-centered Ru and Fe codoped LiNbO₃crystal. Theinfluencing factor of photorefractive effect were studied and discussed in detail. Atlast, the nonvolatile holographic storage properties were measured by two-wavelength technology.Ru and Fe series codoped LiNbO₃crystals were grown by Czochralski method,and the crystals had no macroscopic defect and exhibited good optical homogeneity.In the process of crystal growth, optimum parameters （temperature gradient, pullingspeed and rotating speed） were selected to maintain the flat solid-liquid interface,and the nonuniform component which origined from the solute segregation wasdecreased. The defect structure and ion occupying of Ru:Fe:LiNbO₃crystals wereinvestigated by means of X-ray diffraction, OH-absorption spectra, ultravioletvisible absorption spectra. The results showed that the segregation coefficient of Zrwas close to one. The optical homogeneity of Ru:Fe:LiNbO₃and Zr:Ru:Fe:LiNbO₃crystal was measured via birefringence gradient. The results showed that Zr dpoingwould lead to the decrease of optical quality. The OH-infrared absorption spectrawere measured and fitted by means of Lorentzian function to analysis the Zr ionoccupition. The absorption edge of Zr doped Ru:Fe:LiNbO₃crystal shifted to shortwavelength compared with Ru:Fe:LiNbO₃crystal, which manifested that Zr ionswould enter the lattice by replacingNb4+Li. With the increase of Li-composition, theabsorption edge exhibited blue shift then red shift. When the doping concentrationof Zr ions exceeded its threshold Zr4+would occupy Li and Nb at the same time,Zr3+-Zr-Li Nbcomplex could form and maintained charge balance. The ions replacingmodel was proposed.The photorefractive performance of Ru-Fe series codoped LiNbO₃crystals were investigated by means of conventional two-wave coupling experiment. Thefactors which could affect the photorefractive properties of the crystals such as theincident light wavelength, Zr doping concentration, oxidation or reduction treatmentand Li/Nb ratio in the crystals were discussed. The results showed that forRu:Fe:LiNbO₃crystal, the photorefractive parameters including diffractionefficiency, response time, recording sensitivity and dynamic range at blue light（476nm） were all better than those at red light （633nm）. In addition, doping Zr ionsinto Ru:Fe:LiNbO₃crystals could dramatically enhance the blue photorefractiveproperties. When the Li/Nb ratio in Zr:Ru:Fe:LiNbO₃crystal was close tostoichiometric proportion, the response time would be further shortened. Theimprovement mentioned above was attributed to the decreasing concentration ofintrinsic defects （antisite Nb and Li vacancy）.The light-induced scattering resistance ability of Ru-Fe series codoped LiNbO₃crystals was studied by means of transmitted beam pattern distortion and light-induced scattering exposure energy flux. The influence of Zr doping, oxidation orreduction and Li/Nb ratio in the crystals on the light-induced scattering resistancewas investigated systematically. The results showed that light-induced scattering inas-grown Ru:Fe:LiNbO₃crystal was weaker than that in oxide Ru:Fe:LiNbO₃crystal.Additionally, Zr doping and increasing Li-composition could suppress the light-induced scattering in LiNbO₃crystals.The nonvolatile holographic storage of Ru:Fe:LiNbO₃crystal was measured bymeans of two-wavelength and two-color nonvolatile technology. The dominantcarries of as-grown Ru:Fe:LiNbO₃and oxide Zr:Ru:Fe:LiNbO₃crystal at476nmirradiation was holes, while the dominant carries at633nm irradiation was electrons.The nonvolatile experimental results showed that enhanced nonvolatile storageproperties were obtained in two-wavelength nonvolatile storage. This was attributedto the merits of direct writing, being in the same phase between deep trap centersand shallow trap centers as well as stronger absorption at476nm wavelength than633nm wavelength. Then the nonvolatile properties of Zr doped Ru:Fe:LiNbO₃crystals were studied via two-wavelength nonvolatile technology. Compared withthe properties of two-wavelength and two-color nonvolatile technology crystal, Zrdoping could greatly improve the nonvolatile storage properties, andZr:Ru:Fe:LiNbO₃crystal was outstanding medium for holographic storageapplication.更多还原