PbMoO4晶体生长基元和生长习性的高温拉曼光谱研究

应用高温拉曼光谱研究了PbMoO₄熔体中的生长基元.通过对不同温度下PbMoO₄晶体拉曼光谱和熔点温度附近熔体高温拉曼光谱的研究,发现PbMoO₄熔体中存在Pb²⁺阳离子和［MoO₄］^2－阴离子生长基元.进一步讨论了PbMoO₄晶体生长基元和各个低指数晶面间的相互作用,解释了晶体的生长习性和枝晶生长的原因,并指出:PbMoO₄晶体生 关键词： 钼酸铅晶体 枝晶 籽晶取向 拉曼光谱     

掺铥钨酸镱钾激光晶体结构模拟及振动光谱

采用泡生法生长了掺铥钨酸镱钾（KTm_0.1Yb_0.9（WO₄）₂）激光晶体。利用X射线单晶衍射法和X射线粉末衍射法研究了KTm_0.1Yb_0.9（WO₄）₂晶体的物相与结构。采用X射线单晶衍射法并结合Diamond晶体结构绘图软件,获得了晶体内部结构模型图：该晶体是由WO₆、TmO₈/YbO₈和KO₁₂基团组成。W₂O₁₀二聚体通过WOW单氧桥相连,在平行于c轴方向上形成（W₂O₈）_n多重带。ReO₈和KO₁₂多面体共顶相连,沿[101]和[110]方向形成了具有二维层结构的延长带。X射线粉末衍射分析表明：该晶体具有低温β相双钨酸盐结构,属于单斜晶系,空间群C2/c;计算了晶胞参数、晶粒尺寸和结晶度。测试了晶体的振动光谱,对各个峰值的红外和拉曼活性及分子振动情况进行了归属,进一步验证了晶体中WO₆原子基团及单氧桥（WOW）和双氧桥（WOOW）的存在。     

钨酸铅晶体中与铅空位有关的电子结构和色心模型研究

根据密度泛函理论对钨酸铅晶体中铅空位周围的晶格进行了结构优化，计算得到铅空位周围的晶格结构、电子态密度分布和偏振吸收光谱；计算结果表明钨酸铅晶体中铅空位的两价负电性是通过铅空位周围的氧共同抓获两个空穴来维持局部电中性的，即铅空位周围形成的色心模型为［O₂^3--V_Pb^2--O₂^3-］，不同的氧离子抓获空穴方式不同形成不同的色心，对应不同的吸收带；根据吸收带的偏振性质，提出了各个 关键词： 钨酸铅晶体 色心模型 电子结构 偏振特性     

铁电晶体PbxBa1-xNb2O6和掺Li,Na的PbxBa1-xNb2O6的结构和电弹张量的测定

用提拉法从熔体中生长出Pb_0.37Ba_0.63Nb₂O₆和Pb_0.30Ba_0.533Na_0.306Li_0.028Nb₂O₆两种铁电单晶。用X射线衍射方法分析了两种单晶的结构,结果表明,室温时两种晶体都属于四方晶系点群4mm。测定晶格参数得PBN晶体的a=12.493?和c=3.98?;掺Li,Na的PBN晶体的a=12.493?和c=3.970?。测定了两种晶体全部各52个电弹张量的分量,结果表明PBN晶体具有优良的压电性,其中压电系数d₁₅=108×10^-12C/N。这种晶体很有希望用作与厚度切变模式有关的压电换能器材料。掺Li,Na的PBN晶体的介电常数显著降低,而铁电居里点有明显的提高。 关键词：     

Bi4Ge3O12晶体及其熔体结构的高温拉曼光谱研究

研究了BGO晶体在不同温度下(在300—1323 K的温度范围)的拉曼光谱及其熔体的高温拉曼光谱，分析了BGO晶体结构随温度变化的规律及BGO熔体的结构特征.随着温度的升高，BGO晶体的拉曼光谱谱峰都不同程度地向低波数方向移动，也存在不同程度的展宽，同时强度减弱.另外，在BGO熔体中存在［GeO₄］和［BiO₆］的结构基团；但两种结构之间的联键消失，即在熔体中二者是相互独立的生长基元. 关键词： 高温拉曼光谱 熔体 BGO晶体     

掺镧PbWO4闪烁晶体的缺陷研究

利用正电子湮没寿命谱(PAT)和X射线电子能谱(XPS)研究了掺镧所引起的PbWO₄ 晶体缺陷的变化.结果表明：掺镧后,PbWO₄晶体中的正电子捕获中心铅空位(V< sub>Pb)浓度增加,并进一步诱导低价氧浓度的增加.讨论了掺La的作用机制,认为掺 La将抑制晶体中的氧空位,增加铅空位浓度. 关键词： 掺镧钨酸铅晶体 正电子湮没寿命谱 X射线电子能谱 缺陷     

碱金属阳离子对[B3O7]型非线性光学晶体结晶习性的影响

本文利用高温拉曼光谱技术和从头计算的方法, 研究了LiB₃O₅和CsB₃O₅晶体高温熔融体的结构, 分析了碱金属阳离子对熔体结构的影响, 以及熔体结构的差异与LiB₃O₅和CsB₃O₅晶体结晶习性的联系. 结果表明: LiB₃O₅和CsB₃O₅晶体高温熔融体中的结构基团 主要为B₃Ø₇和B₃Ø₆两种不同类型的硼氧六元环; 环内BØ₄ 四面体的数量影响了六元环呼吸振动峰的拉曼频率, 随BØ₄四面体数量的增加六元环呼吸振动峰向低频移动; LiB₃O₅晶体高温熔融体中, BØ₄四面体含量相对较多; 然而, 离子半径相对较大的Cs⁺离子却阻碍了熔体中BØ₄四面体的形成, 造成CsB₃O₅晶体高温熔融体中BØ₄/BØ₃比值的降低. 结合LiB₃O₅和CsB₃O₅晶体生长动力学过程的分析 (Wang D, Wan S M et al. 2011 Cryst. Eng. Comm. 13 5239), 阳离子的不同导致高温熔体中BØ₄四面体数量的差异, 被认为是影响LiB₃O₅和CsB₃O₅晶体结晶习性的重要因素, 有效降低高温熔体中BØ₄四面体的数量, 将是实现LiB₃O₅晶体生长的关键条件. 关键词： 硼酸盐晶体 熔体结构 拉曼光谱 结晶习性     

LiNb3O8晶体的光学性质

本文测定了LiNb₃O₈晶体的透光曲线,肯定了晶体发黑的主要原因是氧空位,以及通过退火消除的方法;确定了晶体中氢键形成的原因是大气中水蒸汽和熔体起反应的结果,真空退火是消除氢键的方法;提出了在纯氧气氛下生长LiNb₃O₈晶体的建议;测定了LiNb₃O₈晶体的光性方位和主折射率,并和LiNbO₃晶体作了比较;讨论了LiNb₃O₈晶体的光性方位和它的结构关系。 关键词：     

斜钨矿结构钨酸铅晶体电子结构和光学的偏振性质研究

利用完全势缀加平面波局域密度泛函近似,计算了完整的白钨矿结构和斜钨矿结构的钨酸铅（PbWO4）晶体的电子结构;模拟计算了复数折射率、介电函数及吸收光谱的偏振特性。分析了各个吸收光谱的峰值所对应的可能的电子跃迁以及钨酸铅晶体的偏振特性。钨酸铅晶体的光学性质的各向异性反映了钨酸铅晶体的品格结构的各向异性。计算结果表明：斜钨矿结构的钨酸铅晶体的光学性质与白钨矿结构的钨酸铅的光学性质之间存在明显的差异。这说明钨酸铅晶体是一种结构敏感的晶体;计算结果为研究钨酸铅晶体的光学性质与晶体结构之间的关系提供理论基础。     

+3价离子掺杂钨酸铅晶体发光性能和微观缺陷的研究

通过透射光谱、x射线激发发射光谱（XSL）的测试，研究了Bridgman法生长的几种不同+3价离子掺杂钨酸铅晶体的发光性能，并利用正电子湮没寿命谱（PAT）和x光电子能谱（XPS）的实验手段，对不同钨酸铅晶体的微观缺陷进行研究.实验表明，不同的+3价离子掺杂，对钨酸铅晶体发光性能的改善不同，并使得晶体中正电子俘获中心和低价氧的浓度发生不同变化.其中掺镧晶体的正电子俘获中心和低价氧浓度均上升，而掺钇和掺铋晶体的正电子俘获中心和低价氧浓度均下降，掺锑晶体则出现了正电子俘获中心浓度上升、低价氧浓度下降的情况.提 关键词： 钨酸铅晶体 +3价离子掺杂 正电子湮没寿命谱 x光电子能谱     

Spectral kinetics of Ce<Superscript>3+</Superscript> ions in double-fluoride crystals with a scheelite structure

The influence of the cation composition on the spectral kinetics of Ce³⁺ ions in double-fluoride crystals with a scheelite structure is studied. The importance of the photodynamic processes induced in these crystals by the exciting radiation is demonstrated. The difference in luminescence quantum efficiency between Ce³⁺ ions in LiYF₄ and LiLuF₄ crystals is found to be due to the different lifetimes of color centers produced in the samples by the exciting radiation and to the different efficiency of the free-carrier recombination at cerium impurity centers. It is shown that Yb³⁺ ions can increase the carrier recombination rate in the crystals.     

Growth and spectral and luminescent properties of a new Cr<Superscript>4+</Superscript>:LiAlGeO<Subscript>4</Subscript> nonlinear crystal

Single crystals of a new promising laser material, Cr⁴⁺-doped germanium eucryptite Cr⁴⁺:LiAlGeO₄, are grown from the melt for the first time. The crystals grown exhibit nonlinear optical properties. Absorption and luminescence spectra of the crystals and their luminescence decay are studied at various temperatures. The luminescence lifetime at 1.2 μ m at 300 K is 10 μ s. Active centers in the crystal are identified, and crystal field parameters are estimated.     

Conversion of broadband thermal radiation in lithium niobate crystals of various compositions

The conversion of the broadband thermal radiation in stoichiometric (R = 1) lithium niobate single crystals that are grown from melt with 58.6 mol % of LiO₂, congruent (R = Li/Nb = 0.946) melt with the K₂O flux admixture (4.5 and 6.0 wt %), and congruent melt and in congruent single crystals doped with the Zn²⁺, Gd³⁺, and Er³⁺ cations is studied. It is demonstrated that the conversion efficiency of the stoichiometric crystal that is grown from the melt with 58.6 mol % of LiO₂ is less than the conversion efficiency of congruent crystal. In addition, the stoichiometric and almost stoichiometric crystals and the doped congruent crystals exhibit the blue shift of the peak conversion intensity in comparison with a nominally pure congruent crystal. For the congruent crystals, the conversion intensities peak at 520 and 495 nm, respectively.     

A study on the influence of ytterbium and impurities on lattice parameters and the phase transition temperature of Czochralski-grown LiNbO3

LiNbO₃ crystals were grown from a congruent melt by the Czochralski method. Special care was taken with respect to purity and an analysis of impurity levels. Present crystals are as pure as 3N-4N. In particular, doping by Yb³⁺ was investigated. An upper limit for the inclusion of Yb³⁺ in LiNbO₃ may be set at 2.5 mol% for a congruent melt. Present results demonstrate the complex interaction between intrinsic and extrinsic defects in LiNbO₃. The variation of lattice parameters supports evidence for the Li⁺ vacancy model and an occupation of Li sites for Yb³⁺. Data on purities, laser properties and analytical methods provide a short review on a field, where analytical results gained by different techniques often may disagree.     

Yb-and Er-Doped single crystals of double tungstates NaGd(WO4)2, NaLa(WO4)2, and NaBi(WO4)2 as active media for lasers operating in the 1.0 and 1.5 μm ranges

Ytterbium-and erbium-doped single crystals of scheelite-like double tungstates NaGd(WO₄)₂, NaLa(WO₄)₂, and NaBi(WO₄)₂ and scheelite CaWO₄ have been grown by the Czochralski method. The dopant concentrations in crystals are measured, and the coefficients of dopant distribution are determined to range from 0.45 to 3. The lifetimes of the Er³⁺ states ⁴ I _11/2 and ⁴ I _13/2 and the Yb³⁺ state ²F_5/2 are measured, and the absorption and luminescence spectra of the crystals are studied in the vicinity of 1.0 and 1.5 μm. The data obtained are compared with the corresponding characteristics of other crystals. The possible use of the crystals studied as active media of solid-state lasers operating in the range 1.0 and 1.5 μm is discussed. __________ Translated from Optika i Spektroskopiya, Vol. 92, No. 4, 2002, pp. 657–664. Original Russian Text Copyright ? 2002 by Subbotin, Zharikov, Smirnov.     

AgGaS2- and Al-doped GaSe Crystals for IR Applications

We report a systematic study of AgGaS₂- and Al-doped GaSe crystals in comparison with pure GaSe and S-doped GaSe crystals. AgGaS₂-doped GaSe (GaSe:AgGaS₂) crystal was grown by Bridgman technique from the melt of GaSe:AgGaS₂ (10.6 wt.%). Its real composition was identified as GaSe:S (2 wt.%). Al-doped GaSe (GaSe:Al) crystals were grown from the melt of GaSe and 0.01, 0.05, 0.1, 0.5, 1, 2 mass % of aluminium. Al content in the grown crystals is too small to be measured. The hardness of GaSe:S (2 wt.%) crystal grown from the melt of GaSe:AgGaS₂ is 25% higher than that of GaSe:S (2 wt.%) crystal grown by a conventional S-doping technique and 1.5- to 1.9-times higher than that of pure GaSe. GaSe:Al crystals are characterized by 2.5- to 3-times higher hardness than that of pure GaSe and by extremely low conductivity of ≤ 10^− 7 Om^− 1 cm^− 1. A comparative experiment on SHG in AgGaS₂-, Al-, S-doped GaSe and pure GaSe is carried out under the pumps of 2.12-2.9 μm fs OPA and 9.2−10.8 μm ns CO₂ laser. It was found that GaSe:S crystals possess the best physical properties for mid-IR applications among these doped GaSe crystals. GaSe:Al crystals have relatively low conductivity which have strong potential for THz application.     

Analysis of the exchange magnetic structure in Pb<Subscript>3</Subscript>Mn<Subscript>7</Subscript>O<Subscript>15</Subscript>

The indirect-coupling model is used to analyze the exchange magnetic structure of Pb₃Mn₇O₁₅ in the hexagonal setting. The ratios of manganese ions Mn⁴⁺/Mn³⁺ in each nonequivalent position are determined. Pb₃(Mn_0.95Ge_0.05)₇O₁₅ and Pb₃(Mn_0.95Ga_0.05)₇O₁₅ single crystals are grown by the solution–melt method in order to test the validity of the proposed model. The structural and magnetic properties of the single crystals are studied. The magnetic properties of the grown single crystals are compared with those of nominally pure Pb₃Mn₇O₁₅.     

Vibrational spectra of Y3Al5O12 crystals grown from Ba- and Pb-based flux systems

The IR and Raman vibrational spectra of yttrium aluminum garnet (YAG) single crystals grown from Ba- and Pb-based flux systems have been recorded. The existence of AlO₄ and AlO₆ characteristic vibrational bands confirms the garnet structure. The spectra of the two samples are compared with the spectra recorded for YAG crystals grown from pure melt and the results are discussed.     

Determination of a pseudo-binary SrSe–Ga2Se3 phase diagram and single crystal growth of SrGa2Se4 compounds

We have investigated chemical reaction processes and thermal characteristics of IIa–III₂–VI₄ compounds in order to grow their single bulk crystals. Up to now, single crystals of Ca and Sr thiogallates have been successfully grown by the melt growth method based on their pseudo-binary phase diagrams. Here, a similar diagram of the SrSe–Ga₂Se₃ system has been constructed for the first time, where a eutectic reaction is found in the range of excess Ga₂Se₃ concentration, and it is shown that the SrGa₂Se₄ compound has a congruent melting point (1110 °C) suitable for the melt growth. A single crystal is grown from the melt by the horizontal Bridgman method. A trial is also made to grow a high-quality single crystal of CaGa₂S₄ already known as being grown easily.     

Investigation of optical homogeneity and photorefractive properties of lithium-niobate single crystals by the Raman-spectroscopy and laser-conoscopy methods

Photorefractive properties and structural and optical homogeneity of (1) LiNbO₃:Cu crystals ([Cu] = 0.015 mas %) grown from a congruent melt, (2) nominally pure stoichiometric crystals grown from a melt with 58.6 mol % of Li₂O (LiNbO_3stoich), and (3) nominally pure congruent crystals (LiNbO_3congr) have been studied using the Raman-spectroscopy method with excitation in the UV, visible, and near-IR ranges; the laser-conoscopy method; and the electron paramagnetic resonance-spectroscopy method. In optically uniaxial LiNbO₃ crystals, a weak optical biaxiality has been revealed, which is attributed to an insignificant deformation of the optical indicatrix. This deformation can be caused both by the initial structural inhomogeneity of crystals and by the photorefractive effect. It has been shown that, under the action of light, charge exchange of copper cations Cu²⁺ → Cu⁺ takes place in the crystal LiNbO₃:Cu ([Cu] = 0.015 mas %). The LiNbO₃:Cu crystal exhibits photorefractive properties not only because of the occurrence of intrinsic defects with electrons localized at them, as is the case with the LiNbO_3stoich and LiNbO_3congr crystals, but also due to the charge exchange of copper cations under the action of the laser radiation.