TGA-CdTe量子点在荧光探针方面应用

以巯基乙酸(TGA)为稳定剂,在加热回流氮气保护条件下制备CdTe量子点,用荧光分光光度计、透射电子显微镜和X射线粉末衍射仪对CdTe量子点进行表征.以该量子点为荧光探针,完善荧光淬灭法测定Cu2+、Hg2和Ag+等重金属离子的方法.考察缓冲溶液的pH值、反应时间、量子点浓度、量子点的稳定性和干扰离子等多种因素对重金属离子测定的影响.在pH值为6.2的三羟甲基氨基甲烷(tris)-盐酸缓冲溶液中,当量子点的浓度为4.2×10-2 μg/L和反应时间为30 min时,测得Cu2、Hg2+和Ag+的线性区间分别为2.3 ～250 μg、3.2～300 μg和4.3～ 150μg,检测下限分别为0.28 μg/L、0.53 μg/L和0.35 μg/L.并发现只有当所测量的重金属离子能与所采用的量子点能生成更难溶于水的沉淀才能引起量子点的荧光淬火,从而可以对此类重金属离子进行定量检测.     

掺铒硼酸钙氧钆(GdCOB:Er)晶体的光谱分析

生长并测量了新型激光晶体GdCa4O(BO3)3:Er(简称GdCOB:Er)的透过谱,计算了Er3+离子在晶体中的吸收截面.由积分吸收截面的公式拟合出唯象强度参量Ω2＝2.531×10-20cm2,Ω4＝2.716×10-20cm2,Ω6＝1.891×10-20cm2,并应用Judd-Ofelt理论计算出振子强度fJ,J、辐射跃迁几率AJ,J、荧光辐射寿命τ及积分发射截面σ.并根据这些光学参量,讨论了GdCa4O(BO3)3:Er晶体用作激光晶体的可能性.     

Nd3+:LiLa(MoO4)2晶体生长、光谱和激光特性

本论文报道了Nd3+:LiLa(MoO4)2晶体生长、光谱和激光特性.采用提拉法生长出尺寸为φ20×34mm3的Nd+3+:LiLa(MoO4)2晶体.应用Judd-Ofelt理论计算了Nd3+离子在Nd3+:LiLa(MoO4)2晶体中唯象强度、自发发射跃迁几率、荧光分支比、辐射跃迁寿命和荧光量子效率.Nd3+:LiLa(MoO4)2晶体的偏振吸收跃迁截面分别为9.52×10-20cm2(π-偏振)和4.46×10-20cm2(σ-偏振).它的偏振发射跃迁截面分别为0.67×10-19cm2(σ-偏振)和1.02×10-19cm2(σ-偏振).在氙灯泵浦下,获得74.4mJ的1.06μm的激光输出,激光阈值为0.676J,激光总效率和斜率效率分别为0.39;和0.48;.     

以巯基乙酸为稳定剂的水溶性CdTe量子点的水热合成及表征

以巯基乙酸为稳定剂,采用水热合成方法在140℃下合成水溶性CdTe量子点.研究了不同的反应时间、反应温度、反应前驱体pH值、前驱体的配比、前驱体的浓度对CdTe量子点光学性质的影响.采用TEM、XRD、紫外-可见吸收光谱和荧光光谱等技术对所制得产品进行表征.结果表明:当反应前驱体n(Cd2+∶TGA∶ HTe-)=1.0∶2.0∶0.1,C(Cd2+) =2.63×10-3mol/L,反应温度为140℃,pH值为12.0条件下,所制的CdTe量子点的荧光漆发射波长在512 ～559 nm范围内连续可调,量子产率较高(44.9;),半峰宽较窄达(FWHM=50 nm、EM=547.0 nm).与回流方法制备的水溶性CdTe量子点相比,利用水热反应釜的合成方法简单,CdTe量子点生长速度快,70 min就可生长到2.5 nm,粒径较均匀,荧光强度强,能够为免疫层析试纸条的组装提供性能较好的荧光标记物.     

掺铒近化学计量比铌酸锂晶体的生长与光谱性质

利用提拉法,在富锂熔体中生长了质量良好的掺铒近化学计量比铌酸锂单晶,生长的晶体尺寸为35×25mm,测量了晶体的室温吸收谱,并根据Judd-Ofelt理论,拟合出晶体场唯象强度参数:Ω2＝5.37×10-20cm2,Ω4＝2.98×10-20cm2,Ω6＝1.92×10-20cm2.计算了各能级的跃迁辐射几率AJ,J',振子强度PJ,J',辐射寿命τ,荧光分支比βJ'等,并根据这些光学参量讨论了该晶体的部分性能和应用前景.     

Nd:Ca10 K(VO4)7激光晶体的生长及光谱性质

采用固相法合成多晶粉末原料,并用提拉法(Czochraski)生长出尺寸约为φ20 mm×20mm、光学质量优良的Nd:Ca10K(VO4)7晶体.采用电感耦合等离子体原子发射光谱法(ICP)测定了Nd3 、K 离子在晶体中的掺杂浓度,并据此计算出其有效分凝系数Keff分别为1.25、0.73.测定了晶体的热膨胀系数,约为αa=7.9×10-6K-1,αc=11.3×10-6K-1;维氏硬度为358.3VDH.在室温下测定了Nd:Ca10K(VO4)7晶体的偏振吸收谱、偏振荧光谱及荧光寿命,并用J-O理论计算了其光谱参数.结果表明,该晶体在810 nm处的吸收半峰宽为11 nm,其吸收截面为5.06×10-20cm2;在1069nm处具有较大的发射截面,约为1.72×10-19cm2.同时,该晶体还具有比较弱的浓度猝灭效应.这些特点表明该晶体较适合用作微片激光材料.     

掺钬铌酸锂晶体光谱性能研究

采用提拉法得到了纯LiNbO3和掺杂量为2mol;的Ho:LiNbO3晶体.测试了Ho:LiNbO3晶体的吸收光谱、光致发光光谱,采用620nm激发波长得到了523nm的上转换荧光.利用Judd-Ofelt理论计算出在LiNbO3中的强度参数Ω2=27.4×10-20 cm2、Ω4=7.45×10-20 cm2、Ω6=27.1×10-20 cm2,并由此计算了5G4→5I8、5S2→5I7、5F3→5I8处的自发辐射跃迁几率和积分发射截面.     

水热法合成Cu-In-Zn-S量子点及其荧光性能研究

通过水热法制备了Cu-In-Zn-S (CIZS)四元量子点,采用X射线衍射仪(XRD)、能谱仪(EDS)、透射电子显微镜(TEM)、荧光分光光度计(PL)研究了不同反应温度和Cu/In摩尔比对CIZS量子点的物相组成、显微形貌以及荧光性能的影响,同时利用傅里叶变换红外光谱仪(FT-IR)对CIZS量子点的表面性质进行表征.结果 表明,量子点颗粒在水溶液中呈类球型并且具有良好的分散性,粒径大小为3～4 nm.合成的CIZS量子点具有优异的荧光性能,随着反应温度的升高,量子点的荧光强度逐渐增强;当反应温度为110℃时,量子点的荧光强度最高;然而,过高的反应温度造成了In2S3杂质相的形成,荧光强度随之降低.此外,随着Cu/In摩尔比的减小,CIZS量子点的发光峰位由675 nm蓝移至644 nm,同时量子点的荧光强度逐渐提高;当n(Cu)/n(In)=1∶7时,荧光强度达到最高值.同时,量子产率(QYs)达到最大值6.2;.基于CIZS量子点的LED成功实现发光,其中显色指数达81.2,发光效率为36.8 lm/W,表明了CIZS量子点在照明领域良好的应用前景.     

长寿命水溶性CdS/ZnS核-壳量子点的合成及表征

以一锅法合成的CdS量子点为核心,采用单源分子前驱体法成功制备了高质量的油溶性CdS/ZnS核-壳量子点,量子点荧光量子产率高达43.7;,荧光寿命为306 ns.进一步用谷胱甘肽作为相转移剂,将油溶性CdS/ZnS量子点成功转入水相.采用紫外-可见吸收光谱(UV-vis)、荧光光谱(PL)、时间分辨荧光光谱(TRF)、透射电镜(TEM)和X-射线粉末衍射(XRD)对量子点的光谱性质和形貌、结构进行表征.结果表明:谷胱甘肽修饰的量子点水溶性好,粒径均匀,分散性良好,荧光量子产率高,荧光寿命长,显示了较好的生物分析应用前景.     

PSN-PMN-PT∶Er3+晶体Judd-Ofelt理论分析

为了探索Er3+在铁电晶体场中的发光特性,采用高温溶液法生长了Er3+掺杂Pb(Sc1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3弛豫铁电单晶.该晶体在紫外-可见-近红外吸收光谱380～1800 nm波段出现了7个吸收峰;在980 nm泵浦光源照射下,该晶体的发射光谱出现了强绿光和强红光上转换发射带,分别对应于Er3+的4S3/2→4I15/2和4F9/2→4I15/2跃迁;利用Judd-Ofelt理论计算了晶体的振子强度三参数(Ω2＝2.54×10-20 cm2,Ω4＝1.36×10-20 cm2,Ω6 ＝2.38× 10-20 cm2)以及Er3+在PSN-PMN-PT晶体场中的跃迁几率、能级寿命和荧光分支比.研究结果表明 PSN-PMN-PT∶Er3+弛豫铁电晶体是一种新型发光晶体.     

Development of Pauling's concepts of geometric characteristics of atoms

The evolution of the geometric characteristics introduced by Pauling and their dependence on the specific features of the structure and chemical bonds have been considered. The values of the covalent and van der Waals radii are given as well as their relationships and mutual transitions.     

Relationship of Morphological Types of Dynamic Forms of Crystals

Crystallography Reports - The relationship of morphological spectra (sets of data on the morphological types of real polyhedral crystals and their probabilities under current physicochemical...     

A SAXS study of kinetics of aggregation of silica sols

SAXS in situ experiments on the evolution of TMOS solutions during hydrolysis and polycondensation lead to power laws with scaling exponents ≈ 2. It is suggested that this could be the result of the polydispersity of the samples and that only an apparent fractal dimension can be obtained in this way. Kinetic studies tend to indicate that agglomeration in the sol is the result of a diffusion-controlled process.     

Study of the possibility of interactive control of the surface profile of X-ray optical elements

We investigate the possibility of controlling the curvature parameters of parabolic mirrors that are modular elements of two types consisting of a base and thin inserts placed at the opposite side of the work surface. In the first type of modular elements, bending is controlled by the difference in the coefficients of the thermal expansion of the base and inserts. In the second type of elements, the profile is changed by the piezoelectric straining of the inserts under an electric field. A correlation is established between the parameters of modular elements and their surface curvature profile.     

A review of measurement of thermophysical properties of silicon melt

Measurements of thermophysical properties of Si melt and supplementary study of X-ray scattering/diffraction by the authors' group were reviewed. The values obtained differed variously from those of literature. Density was 2–3% larger, surface tension 20–30% smaller, viscosity up to 40% larger, electrical conductivity 8% smaller, spectral emissivity more or less in good agreement with literature values, and thermal diffusivity a few percent larger. An anomalous density jump was found near the melting point. Surface tension and viscosity also showed anomaly. A strange time-dependent change of density was observed over 3 h after melting. X-ray analyses suggested a slight change in local atom ordering, but showed no sign of cluster formation. An addition of 0.1 at% gallium caused the density jump to disappear, while that of boron caused no change. An EXAFS study of the former melt indicated a strong interaction between Ga and Si atoms as if molecules of GaSi₃ existed. The implications of the measured properties are a possibility of soft-turbulence in an Si melt in a relatively large crucible, a more complicated manner of intake of oxygen depleted molten Si from the free surface region to underneath the growing crystal, and a relaxation of the melt after melting arising from trapped gas species.     

Mechanism of thermal expansion of structural modifications of zinc pyrovanadate

Crystal chemical characteristics of the α and β modifications of Zn₂V₂O₇ are calculated based on in situ high-temperature X-ray measurements. The expansion of the structure is found to be strongly anisotropic up to the negative volumetric thermal expansion of the α-Zn₂V₂O₇ unit cell in the temperature range of 300–600°С, α _V =–17.94 × 10^–6 1/K. The transformations of the “hard” and “soft” sublattices with an increase temperature and at the phase transition are considered in detail. It is shown that the negative volumetric thermal expansion of α-Zn₂V₂O₇ is due to the degeneracy of the zigzag-like shape of zinc–oxygen columns at constant distances between their vertices.     

Generation of crystal structures of heteromolecular compounds by the method of discrete modeling of packings

Within the method of discrete modeling of packings, an algorithm of generation of possible crystal structures of heteromolecular compounds containing two or three molecules in the primitive unit cell, one of which has an arbitrary shape and the other (two others) has a shape close to spherical, is proposed. On the basis of this algorithm, a software package for personal computers is developed. This package has been approved for a number of compounds, investigated previously by X-ray diffraction analysis. The results of generation of structures of five compounds—four organic salts (with one or two spherical anions) and one solvate—are represented.     

Dependence of the parameters of equations of viscous flow on chemical composition of silicate melts

The temperature dependence of viscosity of silicate melts is discussed in the framework of the Avramov–Milchev (AM) equation. The composition is described by means of two parameters: the molar fraction, x, and the “lubricant fraction”, l. The molar fraction is the sum of the molar parts x_i of all oxides dissolved in SiO₂, the molar fraction of the latter being 1 ? x. It is shown that, with sufficient precision, two of the parameters of the AM equation can be presented as unique functions of the molar fraction. On the other hand, x is not sufficient to determine properly the reference temperature T_r , at which viscosity is η_r = 10¹³ [dPa.s]. Therefore, additional parameter, “lubricant fraction” l, is introduced. For each of the components, l_i is a product of molar part x_i and a specific dimensionless coefficient 0 ≤ k_i ≤ 1 accounting for the specific contribution of this component to the increased mobility of the system. It is demonstrated that, for l > 0, the reference temperature is related to the “lubricant fraction” l through the reference temperature T_r,SiO2 of pure SiO₂.     

Comparative analysis of two methods of calculation of the orientation of domain walls in ferroelastics

Two types of domain-wall equations are analyzed: the equations derived by the Sapriel method and the equations obtained by interface matching of the thermal-expansion tensor. It is shown that, for W-type domain walls, these methods yield the same equations. For W′-type domain walls, the equations obtained by different methods coincide for proper ferroelastics and differ for improper ferroelastics.     

Investigation of the Mechanism of Influence of Stress Corrosion on the Development of Macroplastic Instabilities of Aluminum–Magnesium Alloy

Crystallography Reports - Macroscopic jumps of plastic deformation (few percent in amplitude) on creep curves of aluminum–magnesium alloy, caused by a local effect of concentrated solution of...