OH~-吸收带作为铌酸锂晶体缺陷结构的探针

本文报道了一组不同Li/Nb比和另一组不同掺Mg浓度的LiNbO_3晶体室温OH~-吸收带的实验结果,观察到OH~-吸收带的三峰结构及其随Li/Nb比的变化,以及重掺Mg晶体中(6mol％MgO)OH~-吸收带转变为双峰结构,并向高能端移动54cm~(-1)。根据LiNbO_3的晶体结构以及Abrahams和Smyth的缺陷结构模型,对化学计量晶体、一致熔化晶体和掺Mg晶体分别进行讨论。并提出重掺Mg晶体中OH~-吸收带向高能端的移动可能是由于当掺Mg浓度超过阈值后Mg~(2+)离子开始进入Nb位而引起的。     

周期极化掺镁不同组分LiNbO3晶体的研究

利用气相平衡扩散法研制出掺镁不同组分的LiNbO₃晶体，并对其极化特性进行了研究.研究表明晶体的开关电场和自发极化不仅与晶体组分［Li］/［Nb］比有关而且与掺镁量有关，［Li］/［Nb］比为0.973掺入2mol% MgO的近化学比LiNbO₃晶体的开关电场仅为1.8kV/mm，是同成分晶体的1/12，且其极化结构的质量要远好于同成分LiNbO₃晶体和近化学比LiNbO₃晶体. 关键词： 气相平衡扩散 3晶体')" href="#">掺镁LiNbO₃晶体 周期极化     

近化学计量组分掺铒铌酸锂晶体光学特性研究

用气相输运平衡技术成功地制备出了近化学计量组分的Er∶LiNbO₃晶体,系统 地研究了该 晶体的吸收边移动、可见—红外透射谱、荧光光谱的物理特性.与同成分Er∶LiNbO_{3晶体 相比, 近化学计量组分Er∶LiNbO3晶体的吸收边出现了“蓝移”;OH^{-吸收带明显减弱 ;在可见—近红外波段呈现出更高的透过率;同时Er3+离子的发光强度也明显 提高. 这些结果表明近化学组分的Er∶LiNbO关键词： 近化学组分掺铒铌酸锂晶体 -}吸收带')" href="#">OH^-吸收带 透射谱 荧光光谱}     

Fe:Mg:LiNbO3晶体电子结构和吸收光谱的第一性原理研究

基于密度泛函理论的第一性原理, 研究了LiNbO₃晶体以及不同Mg浓度的Fe:Mg:LiNbO₃晶体的电子结构和吸收光谱. 研究结果显示: 掺铁铌酸锂晶体的杂质能级由Fe 的3d轨道和O的2p轨道贡献, 禁带宽度为2.845 eV; 对于Mg, Fe共掺样品, Mg的浓度小于或等于阈值时, 禁带宽度分别为2.901 和2.805 eV; 掺铁铌酸锂晶体的吸收谱在2.3和2.6 eV处分别存在一个吸收峰, 其强度因Mg的浓度不同而发生变化. 研究结果还表明, 不同浓度的Mg对晶体内Fe²⁺和Fe³⁺的浓度以及占位产生了不同的影响. 还提出了光电子的形成不应单独考虑铁的轨道电子态, 而应同时考虑与铁成键的氧的轨道电子态的观点.     

第一原理研究Mn掺杂LiNbO3晶体的磁性和光吸收性质

采用基于密度泛函理论和局域密度近似的第一性原理分析了Mn掺杂LiNbO₃晶体的结构, 磁性, 电子特性和光吸收特性. 文中计算了Mn占据Li位和Nb位体系的形成焓, 对应的形成焓分别为-8.340 eV/atom和-8.0062 eV/atom, 也就意味着Mn 原子优先占据Li位. 这也就意味着Mn原子占据Li位的掺杂LiNbO₃晶体结构更稳定. 磁性分析的结果显示, 其对应磁矩也比占据Nb位的高. 进一步分析磁性的来源, 自旋态密度结果显示: Mn掺杂LiNbO₃晶体的磁性主要源于掺杂原子Mn, Mn原子携带的磁矩高达 4.3 μ_B, 显示出高自旋结构. 由于Mn-3d与近邻O-2p及次近邻Nb-4d 轨道的杂化作用, 计算表明: 诱导近邻O原子及次近邻Nb原子产生的磁矩对总磁矩的贡献较小. 通过光学吸收谱的分析, 得出在可见光区Li位被Mn原子替代以后显示出更好的光吸收响应相比于Nb位. 本文还分析了O空位对于LiNbO₃晶体磁性与电子性质的影响, 结果显示O空位的存在可以增加Mn掺杂LiNbO₃体系的磁性.     

高掺镁铌酸锂晶体的生长和倍频性能

我们通过测定MgO在同成分LiNbO₃中的有效分凝系数、相位匹配温度与MgO浓度之间的关系,找到了使Mg:LiNbO₃晶体的相位匹配温度达到最高的掺MgO配方,并克服了Mg:LiNbO₃晶体在高掺杂生长时易出现生长条纹和脱溶等问题,从而生长出了抗光折变能力强,光学均匀性良好的Mg:LiNbO₃晶体。用于连续泵浦Nd:YAG声-光调Q腔内倍频时,获得了平均功率最高达2瓦的二次谐波输出。 关键词：     

Cr4+在八面体格位中的光谱特性研究

采用提拉法生长了Cr单掺和Cr，Mg共掺Al₂O₃晶体，后者具有900—1600nm的宽带吸收.研究了该吸收带在不同气氛、不同温度退火下的变化规律.通过建立合理的晶格缺陷模型，成功地解释了所有的实验结果，并确定Cr，Mg共掺Al₂O₃晶体红外波段宽吸收带属于八面体格位中的Cr⁴⁺离子. 关键词： 4+离子')" href="#">Cr⁴⁺离子 八面体格位 晶格缺陷     

利用超声脉冲回波重合法测定铌酸锂单晶弹性常数CijE和CijD

本文从基本的压电Christoffel方程出发导出三角晶系3m点群压电晶体弹性常数的表示式。并采用10MHz射频超声脉冲回波重合法测量了沿LiNbO₃不同对称方向传播的声速,结合e_ij和ε_ij⁵给出了LiNbO₃全部弹性常数C_ij^E和C_ij^D。它们是C₁₁^E=19.8 关键词：     

掺氧化镁铌酸锂晶体的损伤阈值分析

在经典的双温模型中引入电子激发、载流子吸收等电离过程,建立了飞秒激光和晶体材料相互作用的理论模型。采用有限差分法数值模拟了在飞秒激光作用下,不同掺杂摩尔分数的Mg O∶Li Nb O3晶体内电子、晶格温度随飞秒激光脉宽、激光能量密度的变化规律。并定量分析了不同掺杂摩尔分数的Mg O∶Li Nb O3晶体材料的损伤阈值随脉宽的变化规律,以及掺杂浓度对晶体损伤阈值的影响。结果表明,在Li Nb O3晶体中掺入适量的Mg O将使载流子迁移率发生变化,进而会影响晶体的损伤阈值。在适当掺杂范围内,掺Mg O的摩尔分数越高,载流子迁移率越大,晶体的损伤阈值越高。因此,实际应用中可通过在Li Nb O3晶体中掺入适量的Mg O来提高晶体的抗损伤能力。     

掺镁铌酸锂晶体结构的研究

通过LiNbO₃：MgO(6.7 mol/kg)晶体在常温和低温下的喇曼光谱分析,研究了掺Mg²⁺后晶体结构的变化情况．研究结果表明,常温下晶格略有畸变,个别的散射峰有耦合现象存在,随温度降低,耦合逐渐减少,但掺Mg²⁺后晶格基本结构并无变化. 关键词：     

Stoichiometry dependence of the OH- absorption band in LiNbO3 crystals

Hydrogen in the form of OH^- ions can be incorporated into LiNbO₃ single crystals during the growth process. The infrared absorption band due to the OH^- defects has been measured at room temperature and a considerable change of the band shape has been observed depending on the crystal composition. The structure of the band found in nearly stoichiometric crystals indicates three slightly different proton sites which can be explained on the basis of the LiNbO₃ crystal structure.     

掺锌LiNbO3晶体的生长及其光学性能

在LiNbO₃中掺进3mol%、5mol%、7mol%ZnO生长Zn:LiNbO₃晶体.测试Zn:LiNbO₃晶体的吸收光谱,研究Zn:LiNbO₃晶体吸收边紫移的机制.测试Zn:LiNbO₃晶体的红外光谱,研究Zn(7mol%):LiNbO₃晶体OH 吸收峰由3484cm^-1移到3530cm^-1的机制.测试Zn:LiNbO₃晶体倍频转换效率和相位匹配温度,研究Zn:LiNbO₃晶体倍频转换效率增强的机制.     

OH-absorption properties of the optical damage region in codoped In/Mg:LiNbO3 crystals with various Li/Nb ratios

OH-absorption properties of the optical damage region in a series of codoped In/Mg:LiNbO₃ crystals with various Li/Nb ratios have been investigated. The OH⁻-associated vibrational peak at 3507 cm⁻¹ is confirmed to occur in crystals with Li/Nb ratio of 0.94. For codoped In/Mg:LiNbO₃ crystals with Li/Nb ratio of 1.05 and 1.20, the OH⁻-associated vibrational peaks are detected at 3536 and 3507 cm⁻¹ as well. A new peak at 3518 cm⁻¹ attributed to a (In_Nb)²⁻-OH⁻-(Mg_Nb)³⁻ defect center is revealed in crystals with Li/Nb ratio 1.38. When the “In-Mg threshold” concentration is reached, the optical damage resistance ability of codoped In/Mg:LiNbO₃ crystals is greatly improved.     

Enhancement of blue holographic properties in Zr4+-doped near stoichiometric Fe:LiNbO3 crystals

The near stoichiometric LiNbO₃ crystals co-doped with ZrO₂ and Fe₂O₃ have been grown from a Li-rich melt (Li/Nb=1.38, atomic ratio) by the Czochralski method in air atmosphere at the first time. The OH^? absorption and UV–vis absorption spectra were characterized to investigate the defect structure of the crystals. The appearances of the 3479 cm^?1 absorption peak and 358 nm absorption edge manifest that the composition of the grown crystal is close to the stoichiometric ratio. The blue holographic properties were also measured by the two-wave coupling experiments. As a result, in the near stoichiometric Zr:Fe:LiNbO₃ crystals, photorefractive response speed, recording sensitivity, and two-wave coupling gain coefficient are significantly enhanced. Meanwhile, the high saturation diffraction efficiency is still maintained. These findings prove that the material of near stoichiometric Zr:Fe:LiNbO₃ crystals are a promising candidate for blue photorefractive holographic recording.     

Influence of post-grown Li-rich and Li-poor vapor transport equilibration on composition, OH− absorption and optical-damage threshold of Mg (5 mol%) : LiNbO3 crystals

Li-rich (Li-poor) vapor transport equilibration (VTE) treatments on a number of Z-cut 0.47 mm thick congruent MgO (5 mol% in melt) : LiNbO₃ crystals were carried out at 1100°C over different durations ranging in 1–172 (40–395) h. Neutron activation analysis shows that neither Li-rich nor Li-poor VTE-induced Mg and Nb loss from the crystal occurred. The Li₂O content in the crystal was measured as a function of VTE duration by the gravimetric method. The Li-rich/Li-poor VTE effects on OH⁻ absorption were studied in comparison with the as-grown crystal. The study shows that the Li-rich VTE results in OH⁻ absorption band annihilation. After further oxidation treatment the band reemerges and peaks at the same wavenumber as that of the as-grown crystal (∼3535.6 cm⁻¹), showing that the MgO concentration in the Li-rich VTE crystal is still above the optical-damage threshold. The Li-poor VTE causes OH⁻ band shift to 3486.3–3491.6 cm⁻¹, indicating that the MgO concentration in all Li-poor VTE crystals is all below the optical-damage threshold. Further successive Li-rich VTE and oxidation treatments on the Li-poor VTE-treated crystal lead the band to shift back to 3535.6 cm⁻¹, showing that the post Li-rich VTE brought the Li-poor VTE-treated crystal above the optical-damage threshold again. It is found that the peaking position, band width, peaking absorption and band area of the absorption at ∼3486 cm⁻¹ all increase monotonously with the decrease of the Li₂O content arising from prolonged Li-poor VTE, and quantitative relationships to the Li₂O content are established for the latter two parameters. The VTE effects on the OH⁻ absorption are conducted with the VTE-induced OH⁻ content alteration and charge redistribution.     

Photorefractive properties for holographic application of Ce:Fe:LiNbO3 crystals with various [Li]/[Nb] ratios

Ce:Fe:LiNbO₃ crystals with various [Li]/[Nb] ratios were grown by the Czochralski method from melts having compositions varying between 48.6 and 58 mol% Li₂O. The Ce, Li and Nb concentrations in the grown Ce:Fe:LiNbO₃ crystals were analyzed by the inductively coupled plasma atomic emission spectrometer (ICP-AES). It was found that as the [Li]/[Nb] ratio increases in the melt, the [Li]/[Nb] ratio in the crystal and the distribution coefficients of Ce ions increase also. The photorefractive properties of the Ce:Fe:LiNbO₃ crystals were experimentally studied by the two-wave coupling method. The results show that as the [Li]/[Nb] ratio increases, the dynamic range decreases, but the photorefractive sensitivity and the signal-to-noise ratio improve. In a coherent volume 0.192 cm³ of a Ce:Fe:LiNbO₃ crystal with [Li]/[Nb] ratio of 1.2, 3800 holograms with 800×600 pixels have been successfully multiplexed in a compact volume holographic data storage system.     

Effect of [Li]/[Nb] ratios on the photorefraction and scattering properties in In: Fe: Cu: LiNbO3 crystals at 488 nm wavelength

The high sensitivity, fast response and the high quality reconstructions are observed in various [Li]/[Nb] ratios In:Fe:Cu:LiNbO₃ crystals at 488 nm wavelength based on the two-beam coupling experiment. The strong blue photorefraction is contributed by the two-center effect and the remarkable characteristic of being in phase between the two gratings recorded in shallow and deep trap centers. The blue photorefraction is enhanced significantly with the increasing of [Li]/[Nb] ratios under the same experimental conditions. The sensitivity S" is reduced to 0.46 J/cm, simultaneously the response time is as fast as 4.4 s and the erase phenomenon is not obvious in In:Fe:Cu:LiNbO₃ crystals which [Li]/[Nb] ratio is 0.986 in crystal. Increasing [Li]/[Nb] ratios improve the damage-resistant ability of the crystals, but lead to a more serious beam fanning. Experimental results definitely show that the near-stoichiometric In: Fe: Cu: LiNbO₃ crystal becomes a promising candidate for blue photorefractive holographic recording.     

Improvement of photorefractive properties in Hf:Fe:LiNbO3 crystals with various [Li]/[Nb] ratios

Photorefractive properties of Hf:Fe:LiNbO3 crystals with various [Li]/[Nb] ratios have been investigated at 488 nm wavelength based on the two-wave coupling experiment. High diffraction efficiency and large recording sensitivity are observed and explained. The decrease in Li vacancies is suggested to be the main contributor to the increase in the photoconductivity and subsequently to the induction of the improvement of recording sensitivity. The saturation diffraction efficiency is measured up to 80.2%, and simultaneously the recording sensitivity of 0.91 cm/J is achieved to in the Hf:Fe:LiNbO3 crystal grown from the melt with the [Li]/[Nb] ratio of 1.20, which is significantly enhanced as compared with those of the Hf:Fe:LiNbO3 crystal with the [Li]/[Nb] ratio of 0.94 in melt under the same experimental conditions. Experimental results definitely show that increasing the [Li]/[Nb] ratio in crystal is an effective method for Hf:Fe:LiNbO3 crystal to improve its photorefractive properties.     

Growth and photorefractive properties of near-stoichiometric In:Fe:Cu:LiNbO3 crystals

The near-stoichiometric LiNbO₃ crystal co-doped with In₂O₃, Fe₂O₃, and CuO has been grown from a Li-rich melt (Li/Nb = 1.38, atomic ratio) by the Czochralski method in air atmosphere for the first time. The OH⁻ absorption spectra were characterized to investigate the structure defects of the crystals. The appearance of the 3506 cm⁻¹ absorption peak manifests that the composition of the grown crystal is close to the stoichiometric ratio. The photorefractive properties were also measured by the two-wave coupling experiments. The results show that the near-stoichiometric In:Fe:Cu:LiNbO₃ crystal has a larger refractive index change, higher recording sensitivity and larger two-wave coupling gain coefficient than those obtained in the congruent In:Fe:Cu:LiNbO₃ crystal under the same experimental conditions. The material of near-stoichiometric In:Fe:Cu:LiNbO₃ crystal is a promising candidate for blue photorefractive holographic recording.