基质晶体的化学键性质与掺杂稀土离子发光特性间关系的研究

本文使用复杂晶体化学键理论对由Eu2+或Ce3+掺杂的复杂基质晶体的化学键性质进行了理论研究，同时对发光稀土离子的发光特性与其在所处晶体中所表现的化学键性质间的关系进行了理论上的探讨，所研究的对象是具有复杂晶体结构的系列晶态物质，其中包括Eu2+掺杂的碱土硼酸盐系列晶体、Eu2+掺杂的碱土硅酸盐系列晶体、Eu2+掺杂的碱土铝酸盐系列晶体，卤化硫硅酸饰系列晶体及Ce3+掺杂的碘化硫硅酸斓晶体等。理论计算的结果表明具有4f~(n+1) 4f ~n5d~1组态间跃迁Eu2+和Ce3+离子之所以在不同基质晶体中表现出不同的发光特性是与它在不同基质晶体中呈现出不同的化学键性质而造成的。更深入的研究发现，在晶体结构和中心离子配位环境非常相似的系列晶体中，’掺杂离子发射光的Stokes位移值与其所取代格位的平均共价性成正比的关系，这是由于Stokes位移的本质是发光离子在发光过程中向基质以光波辐射的形式传递能量，这一能量的大小是由基质的振动频率决定的，而基质的化学键性质恰恰决定着基质的振动频率。在碱土硼酸盐系列晶体中Ba2MgB2O6, BaBe2B2O6 1 Ba2LiB5Ojo和SrB4O7四种晶体所对应的点（Stokes shift vs Fc）处在同一条直线上，而SrA12B207和BaLiBO3晶体所对应的点并没有处在这条直线上。在碱土硅酸盐系列晶体中CaSiO3 1SrSiO3 , BaSiO3三种‘晶体所对应的点处于同一条直线上，而同一系列的Sr2LiSiO4F, BasS1O4Br，BaSSiO4Cl。三种晶体所对应的点却处在另一条直线上，造成这种分组的原因是由于处于同一直线上的晶体属于键性相近的晶体。进一步研究表明掺杂离子发射光的Stokes位移值不仅与所处的晶体有关，还与其在晶体中所处的不同格位的键性有关。在讨论键性与轨道劈裂能之间的关系时发现，化学键性质确实是影响劈裂能大小的一个因素，但由于还存在其它因素影响着轨道的能级劈裂，所以目前我们没能确定出化学键性质与轨道劈裂能之间的定量关系。

Accurate determination of electronic transition energy of carbon nanotubes from the resonant behavior of radial breathing modes and their overtones

The resonant Raman behavior of the radial breathing modes are very useful to analyze the electronic property of carbon nanotubes. We investigated the resonant behaviors of Stokes and anti-Stokes radial breathing mode and its overtone of a metallic nanotube, and show how to accurately determine the electronic transition energy of carbon nanotubes from radial breathing modes and their overtones. Based on the present results, the previously reported resonant Raman behavior of the radial breathing modes of SWINT bundles can be interpreted very well.

Photoluminescence of ZnS clusters in zeolite-Y

Two obvious emissions are observed from the ZnS clusters encapsulated in zeolite-Y. The emission around 355 nm is sharp and weak, locating at the onset of the absorption edge. The band around 535 nm is broad, strong and Stokes-shifted. Both the two emissions shift to blue and their intensities firstly increase then decrease as the loading of ZnS in zeolite-Y or clusters size decreases. Through investigation, the former is attributed to the excitonic fluorescence, and the latter to the trapped luminescence from surface states. The cluster size-dependence of the luminescence may be explained qualitatively by considering both the carrier recombination and the nonradiative recombination rates. Four peaks appearing in the excitation spectra are assigned to the transitions of 1S-1S, 1S-1P, 1S-1D and surface state, respectively. The excitation spectra of the clusters do not coincide with their absorption spectra. The states splitted by quantum-size confinement are detected in the excitation spectra, but could not be differentiated in the optical absorption spectra due to inhomogeneous broadening. The size-dependence of the excitation spectra is similar to that of the absorption spectra. Both the excitation spectra of excitonic and of trapped emissions are similar, but change in relative intensity and shift in position are observed.

ZnS1-xTex混晶的压力光谱

研究了ZnS1-xTex(0.02≤x≤0.3)混晶的静压光致发光谱。每块样品都观察到一个峰值比相应混晶带隙低很多的发光峰，来源于束缚在Ten(n≥2）等电子陷陆上的激子复合发光，且随压力（0．7GPa）而蓝移、发光峰的压力系数比相应混晶带边的都要小，随着Te组分的增加而减小，与混晶带隙压力系数的差别也越来越大。由于压力下与发光峰对应的吸引能量逐渐接近并超过激发光的能量，与发光峰有关的吸收效率降低，发光峰积分强度随着压力增加而减小。据此估算了Ten等电子中心的Stokes位移。发现Stokes位移随着Te组分的增加而减小。

单晶硅化学气相沉积反应器流场初探

对单晶硅化学气相沉积(CVD)反应器在沉积过程中的流场进行了初步分析。通过数值求解三维层流Navier-Stokes方程，研究了反应器内浮力效应所引起的流场对称性破坏。结果表明，由于存在浮力效应，轴对称几何体中也会发生非轴对称流场分布，从而影响单晶硅的均匀生长。

Observation of the resonant Raman behavior of individual single-walled carbon nanotubes

The different resonant Raman scattering process of single-walled carbon nanotubes (SWNTs) has been found between the Stokes and anti-Stokes sides of the radial breathing modes (RBMs), and this provides strong evidence that Raman spectra of some special diametric SWNTs are in resonance with their electronic transitions between the singularities in the one-dimensional electronic density of states in the valence and conduction bands, and other SWNTs axe beyond the resonant condition. Because of the coexistence of resonant and non-resonant Raman scattering processes for different diametric SWNTs, the relative intensity of each RBM does not reflect the proportion of a particular SWNT.

High temperature annealing behaviors of luminescent SIOx : H films

The effects of high temperature annealing on the microstructure and optical properties of luminescent SiOx:H films have been investigated. Micro-Raman scattering and IR absorption, in combination with atomic force microscopy (AFM), provide evidence for the existence of both a-Si clusters in the as-grown a-SiOx:H and Si nanocrystals in the 1170 degrees C annealed films. The dependence of optical coefficients (alpha) on photon energy (h nu) near the absorption edge (E-g) is found to follow the square root law: (alpha h nu)(1/2) proportional to (E-g - h nu), indicating that nano-Si embedded in SiO2 is still an indirect material. A comparison of the deduced absorption edge with the PL spectra shows an obvious Stokes shift, suggesting that phonons should be involved in the optical transition process.

Characterization of CdSe and CdSe/CdS core/shell nanoclusters synthesized in aqueous solution

CdSe nanoclusters overcoated with CdS shell were prepared with macapoacetic acid as stabilizer. The optical properties of CdSe nanoclusters and the influence of CdS shell on the electronic structures of CdSe cores were studied by optical absorption, photoluminescence (PL) and photoluminescence excitation (PLE) spectroscopies. Based on PL and PLE results and the theoretical calculation on fine structure of bandedge exciton, a model of formation of excimer within the small clusters was proposed to explain the large Stokes shift of luminescence from absorption edge observed in PL results. (C) 2000 Elsevier Science B.V. All rights reserved.

Pressure behavior of deep centers in ZnSxTe1-x alloys

We have measured photoluminescence of ZnSxTe1-x alloys (x > 0.7) at 300 K and under hydrostatic pressure up to 7 GPa. The spectra contain only a broad emission band under excitation of the 406.7 nm line. Its pressure coefficients are 47, 62 and 45 meV/GPa for x = 0.98, 0.92 and 0.79 samples, which are about 26%, 7% and 38% smaller than that of the band gap in the corresponding alloys. The Stokes shifts between emission and absorption of the bands were calculated by fitting the pressure dependence of the emission intensity, being 0.29, 0.48 and 0.13 eV for the three samples, respectively. The small pressure coefficient and large Stokes shift indicate that the emission band observed in our samples may correspond to the Te isoelectronic center in the ZnSxTe1-x alloy.

Statistical analysis of microscale gas flows and stock price changes

First, recent studies on the information preservation (IP) method, a particle approach for low-speed micro-scale gas flows, are reviewed. The IP method was validated for benchmark issues such as Couette, Poiseuille and Rayleigh flows, compared well with measured data for typical internal flows through micro-channels and external flows past micro flat plates, and combined with the Navier-Stokes equations to be a hybrid scheme for subsonic, rarefied gas flows. Second, the focus is moved to the microscopic characteristic of China stock market, particularly the price correlation between stock deals. A very interesting phenomenon was found that showed a reverse transition behaviour between two neighbouring price changes. This behaviour significantly differs from the transition rules for atomic and molecular energy levels, and it is very helpful to understand the essential difference between stock markets and nature.

LOCAL BENDING OF THIN FILM ON VISCOUS LAYER

Effects of deposition layer position and number/density on local bending of a thin film are systematically investigated. Because the deposition layer interacts with the thin film at the interface and there is an offset between the thin film neutral surface and the interface, the deposition layer generates not only axial stress but also bending moment. The bending moment induces an instant out-of-plane deflection of the thin film, which may or may not cause the so-called local bending. The deposition layer is modeled as a local stressor, whose location and density are demonstrated to be vital to the occurrence of local bending. The thin film rests on a viscous layer, which is governed by the Navier-Stokes equation and behaves like an elastic foundation to exert transverse forces on the thin film. The unknown feature of the axial constraint force makes the governing equation highly nonlinear even for the small deflection case. The constraint force and film transverse deflection are solved iteratively through the governing equation and the displacement constraint equation of immovable edges. This research shows that in some special cases, the deposition density increase does not necessarily reduce the local bending. By comparing the thin film deflections of different deposition numbers and positions, we also present the guideline of strengthening or suppressing the local bending.

零攻角NADTPS重构高超声速流场气动力/热研究

长时间、远距离高超声速飞行要求飞行器设计兼顾减阻和防热特点,论文提出无烧蚀自适应减阻防热新概念(NADTPS)并展开相关研究。NADTPS基于支杆-钝头体结构重构流场,利用侧向射流重点防护支杆头部。本文通过数值求解二维轴对称Navier-Stokes方程,对零攻角下NADTPS重构流场进行模拟,研究流场基本特征、气动力/热特性,分析新概念的减阻和防热机理。

超声速平板绕流的全流域阻力特性研究

超声速流动中摩擦阻力的准确预测一直是气动研究中的难点。本文以零攻角的平板绕流为对象，结合传统的CFD方法求解Navier-Stokes方程和直接模拟Monte-Carlo（DSMC）方法模拟粒子的微观运动，研究平板在超声速来流下的全流域阻力特性。研究发现，在超声速流中会产生激波-边界层相互干扰作用并随着来流马赫数的增加而加强，同时平板前缘存在非平衡效应显著的区域；努森数的增大使激波和边界层均增厚，粘性作用增强，非平衡区的范围增大，非平衡强度增强，而激波强度减弱；最后通过拟合连续流条件下的摩阻系数和修正自由分子流结果，结合桥函数，获得了全流域范围内均有效的平板阻力系数表达式。

支杆-钝头体带攻角飞行流场和“军刺”挡板作用机理研究

本文通过三维Navier-Stokes方程的数值求解，研究了支杆-钝头体结构在10°攻角M∞=6.0飞行条件下的流场结构和特点，指出其气动力特性恶化的原因，提出采用“军刺”挡板改善流场和气动力特性，并通过对比两种不同挡板作用下的流场和气动力特性变化分析其作用机理，发现“军刺”挡板结构分割流场抑制三维效应形成的周向流动，迎风面形成稳定的回流区和剪切层结构，将迎风面锥激波推离轴线，降低钝头体肩部流动结构相互作用强度，并在一定程度上缓解背风面流动干扰，明显改善支杆-钝头体带攻角飞行时的气动力特性。

Heat Transfer Problems Induced By Multi-shocks Interaction

Numerical simulations of the multi-shock interactions observable around hypersonic vehicles were carried out by solving Navier-Stokes equations with the AUSMPW scheme and the new type of the IV interaction created by two incident shock waves was investigated in detail. Numerical results show that the intersection point of the second incident shock with the bow shock plays important role on the flow pattern, peak pressures and heat fluxes. In the case of two incident shocks interacting with the bow shock at the same position, the much higher peak pressure and more severe heat transfer rate are induced than the classical IV interaction. The phenomenon is referred to as the multi-shock interaction and higher requirements will be imposed on thermal protection systems.