钽铌酸锂晶体的布里渊散射研究

研究了钽铌酸锂(LiTa_xNb_(1-x)O_3,x=0.0013,0.0052,0.015,0.06)晶体在室温的布里渊散射.给出了它们的弹性刚度常数和压电应力常数.测量了一种组份晶体的布里渊散射频移在50K～580K范围内的温度特性.发现某些声子散射谱中除三个正常峰外还存在一个异常峰.     

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}     

纯铌酸锂晶体红外光谱的低温研究

测量了同成分纯铌酸锂的低温红外光谱,发现低温下铌酸锂晶体将会出现位于3200 cm^-1左右的新红外吸收峰.研究发现该峰与晶体中的氢离子无关,并且其峰强和峰形都随温度的升高发生复杂的变化.基于上述实验结果,认为该峰应该起源于电子在相邻的小极化子（Nb⁴⁺_Li）和自由极化子（Nb⁴⁺_Nb）之间的跃迁.另外,通过拟合发现新红外吸收峰可分解成三个高斯峰,这三峰应归因于能量有细微差别的三种跃迁. 关键词： 铌酸锂 红外吸收光谱 杂质缺陷     

掺镁铌酸锂晶体的缺陷结构及其结晶化学分析

根据铌酸锂晶体本征缺陷的Ｌｉ空位模型，提出了掺镁铌酸锂晶体的缺陷结构模型；计算出了掺镁铌酸锂晶体中Ｌｉ_２Ｏ，Ｎｂ_２Ｏ₅的含量、［Ｌｉ］／［Ｎｂ］比以及晶体的密度随掺镁浓度的变化关系．计算结果与文献中报道的实验结果相符合 关键词：     

掺铁铌酸锂晶体中光致散射的锂组分和温度依赖关系研究

研究了单掺铁铌酸锂晶体的光致散射行为随锂组分以及温度的变化关系.实验表明,随晶体组分的升高,光致散射得到了大幅抑制;不同组分晶体光致散射被完全抑制的温度不同.由此提出掺铁铌酸锂晶体在48.9 mol%-49.3 mol%范围内可能存在一临界锂组分,当晶体组分超过这一临界组分时,晶体光致散射被大幅抑制,而光致散射行为的温度依赖关系明显改变.     

250 keV He+ 离子注入钽酸锂改性研究

室温下,将能量为250 keV He+ 离子注入z 切钽酸锂单晶,注量范围5.0x1014~5.0x1016 He+/cm2,应用三维轮廓仪、X射线衍射(XRD)、紫外可见(UV-Vis ) 光学吸收谱对未注入和注入样品进行了表征和分析。分析结果表明,在注量达到5.0x1016He+/cm2 时,样品表面出现大量凸起条纹,同时晶格沿着[001] 方向出现明显肿胀,吸收边则表现出明显的注量相关性。注入样品在空气中放置60 d后,最高注量的样品表面原来凸起的条纹变为细长的裂纹,晶格应变及光学吸收边均出现较大的恢复。讨论了样品表面形貌、晶格应变和光学吸收边与He 行为的关系。The effects of 250 keV He + implantation in the fluence from 5.0x1014 to 5.0x1016 He+/cm2 on lithium tantalate at room temperature were investigated by 3D surface profiler, XRD and UV-Vis optical absorption spectroscopies.The experimental results show that a large number of raised stripes appear on the surface of the sample and the significant lattice swelling occurs along the direction [ 001 ] at the fluence of 5.0x1016 He+/cm2. The dependence of changes absorption edge on the fluences was revealed. After the samples had been exposed to the air for 60 days, the raised stripes on the surface have evolved into narrow cracks. Furthermore, the lattice strain and the optical absorption edge has also recovered dramatically. The relationship between surface morphology, lattice strain, optical absorption edge and behaviorof He-ions was discussed.     

掺锰铌酸锂晶体第一性原理研究

利用第一性原理研究了Mn:LiNbO3晶体的电子结构和光学性质。结果表明,Mn掺杂产生了杂质能级,主要由Mn的d态轨道贡献。杂质能级与导带之间的带隙小于理想LiNbO3晶体导带与价带之间宽度,降低了电子跃迁所需能量。同时,掺杂也降低了各原子的电子轨道能量。晶体中最高占据轨道不再是O的2p轨道,而是Mn的d 轨道。掺杂离子在晶体中同时充当电子的施主与受主。静态介电常数在掺杂后有明显的增大。Mn的掺杂使晶体在可见光区域的光学性质产生变化,并使晶体的吸收谱在可见光区域产生吸收峰。     

掺铁铌酸锂晶体第一性原理研究

利用第一性原理研究了Mn:LiNbO3晶体的电子结构和光学性质。结果表明,Mn掺杂产生了杂质能级,主要由Mn的d态轨道贡献。杂质能级与导带之间的带隙小于理想LiNbO3晶体导带与价带之间宽度,降低了电子跃迁所需能量。同时,掺杂也降低了各原子的电子轨道能量。晶体中最高占据轨道不再是O的2p轨道,而是Mn的d 轨道。掺杂离子在晶体中同时充当电子的施主与受主。静态介电常数在掺杂后有明显的增大。Mn的掺杂使晶体在可见光区域的光学性质产生变化,并使晶体的吸收谱在可见光区域产生吸收峰。     

双掺杂铌酸锂晶体的第一性原理研究

本文利用第一性原理研究了Mn:Fe:LiNbO3晶体、Mn:Ru:LiNbO3晶体和Fe:Ru:LiNbO3晶体的电子结构和光学性质.通过对电子结构的分析,发现杂质能级的深浅与掺杂元素原子序数有关.原子序数越大,杂质能级越深.通过对Mn:Fe:LiNbO3晶体、Mn:Ru:LiNbO3晶体和Fe:Ru:LiNbO3晶体...     

双掺杂铌酸锂晶体的第一性原理研究

本文利用第一性原理研究了 晶体、 晶体和 晶体的电子结构和光学性质。通过对电子结构的分析,发现杂质能级的深浅与掺杂元素原子序数有关。原子序数越大,杂质能级越深。通过对 晶体、 晶体和 晶体的吸收谱进行分析,并与单掺杂 晶体的吸收谱进行比较,发现双掺杂在可见光区域吸收率明显提高,约为单掺杂的3倍。 晶体分别在380nm和590nm处形成吸收峰, 晶体可见光区域吸收率比 以及 晶体高,分别在450nm附近和660nm附近出现吸收峰, 晶体在430nm到600nm之间区域都有较高的吸收率,并在770nm的长波范围有一小的吸收峰。计算结果与双色全息存储（双光子全息存储）所用记录光的波长相符。     

近化学计量比钽酸锂畴反转特性研究

采用助熔剂提拉法生长了非掺杂及掺镁近化学剂量比钽酸锂晶体.氢氟酸腐蚀晶片的金相显微镜观察结果显示,化学剂量比钽酸锂的畴结构为六边形.利用自行研制的极化设备对晶体进行极化实验,采用外加短脉冲极化电场,测定了近化学计量比钽酸锂单晶的畴反转特性,得到了完全反转的畴结构. 关键词： 近化学剂量比钽酸锂 畴结构 矫顽场 极化电流     

Surface ablation of lithium tantalate by femtosecond laser

We report measurements of the laser induced breakdown threshold in lithium tantalate with different number of pulses delivered from a chirped pulse amplification Ti: sapphire system. The threshold fluences were determined from the relation between the diameter D² of the ablated area and the laser fluence F₀. The threshold of lithium tantalite under single-shot is found to be 1.84 J/cm², and the avalanche rate was determined to be 1.01 cm²/J by calculation. We found that avalanche dominates the ablation process, while photoionization serves as a free electron provider.     

a-Si:H films: Influence of P- and B-doping on infra-red absorption bands

Summary The infra-red spectra of P- and B-doped hydrogenated amorphous silicon films grown by means of an evaporation method have been measured. The SiH _n stretching and wagging (or rocking) absorption bands have been examined by varying the dopant content measured by Auger analysis. On increasing the doping, a reduction of hydrogen content has been noticed with an enhancing of zeroth-order moment of Si-H stretching at the expense of the Si-H₂ one. Analogous results for B-doped films have been observed. Since no frequency shift towards higher frequencies of the stretching bands has been measured, the observed changes of the intensity of the bands have been attributed to structure modifications rather than to variations in the electronegativity in the neighbours of the silicon atom. In particular, the monohidride configuration with an overall decrease in the number of defects seems to be favoured by the deposition technique adopted. This work was supported in part by GNSM-CNR, M.P.I. and CNR ?Progetto Finalizzato Energetica?.     

The composition dependence and new assignment of the Raman spectrum in lithium tantalate

The Raman scattering spectra of lithium tantalate crystals with different compositions were investigated. The comparison of the Raman data obtained for the congruent and the near-stoichiometric crystals reveals some differences in the shape and the number of Raman peaks, which lead to a new assignment of the long-wavelength optical phonons. And quantitative relationships between the linewidth of Raman peaks (142 cm⁻¹ for E-phonon and 861 cm⁻¹ for A₁-phonon) and the crystal composition were firstly presented. Two local Raman lines, 278 and 750 cm⁻¹, were found for the congruent crystals and attributed to the intrinsic defects, Li vacancy and anti-site Ta ion, respectively.     

Quantitative evaluation of the electro-optic effect and second-order optical nonlinearity of lithium tantalate crystals of different compositions using Raman and infrared spectroscopy

Nominally pure lithium tantalate (LiTaO₃) crystals with different chemical compositions were characterized by Raman scattering, infrared reflection, and infrared absorption spectroscopy. In these crystals specific phonon bands are correlated to electro-optic and nonlinear optical properties. The electro-optic and nonlinear optical coefficients were determined and the data are compared with literature values obtained by direct measurements. Our measurements are in good accordance with the literature data, which opens up a new possibility for fast and easy estimation of electro-optic and nonlinear optical performance of newly developed LiTaO₃-based materials modified by stoichiometry. PACS 42.70.Mp; 78.20.Jq; 78.30.-j     

Co,Zn共掺铌酸锂电子结构和吸收光谱的第一性原理研究

利用基于密度泛函的第一性原理的计算方法,研究了Co单掺及Co和Zn共掺LiNbO_3晶体的电子结构和吸收光谱.研究显示,各掺杂体系铌酸锂晶体的带隙均较纯铌酸锂晶体变窄. Co:LiNbO_3晶体禁带宽度为3.32 eV; Co:Zn:LiNbO_3晶体, Zn的浓度低于阈值或达到阈值时,禁带宽度分别为2.87或2.75 eV. Co:LiNbO_3晶体在可见-近红外光波段2.40, 1.58, 1.10 eV处形成吸收峰,这些峰归结于Co 3d分裂轨道的跃迁;加入抗光折变离子Zn~(2+),在1.58, 1.10 eV处的吸收峰增强,可以认为Zn~(2+)与Co~(2+)之间存在电荷转移,使e_g轨道电子减少,但并不影响t_(2g)轨道电子.结果表明,晶体中的Co离子在不同共掺离子下可充当深能级中心(2.40 eV),或可充当浅能级中心(1.58 eV),两种情况下,掺入近阈值的Zn离子均有助于实现优化存储.     

Influence of Mg doping on the dielectric properties of MgO-doped lithium niobate

The dielectric function of MgO-doped lithium niobate (LN:Mg) has been calculated, which depends on the angular frequency and Mg concentration. On the basis of our experimental data and the defect structure models, the substitution of Li ions by Mg ions will strongly influence the dielectric properties of LN:Mg.