Luminescent properties of La2LiTaO6:Mn4+ and its application as red emission LEDs phosphor

A novel phosphor, Mn⁴⁺ doped La₂LiTaO₆, was developed by solid-state reaction method. The luminescent spectra and emission efficiencies of La₂LiTaO₆:Mn _x ⁴⁺ (x = 0.001, 0.003, 0.005 and 0.01) were discussed. The effects of co-doped charge compensation ions, M = Mg²⁺, Ca²⁺, Na⁺, were investigated, respectively. The excitation spectra indicated that La₂LiTaO₆:Mn⁴⁺ could be effectively excited by both NUV light and blue light. The emission spectra of the phosphor exhibit a broadband ranging from 670 to 720 nm with the maximum at about 709 nm in deep red region. The co-doping of Mg²⁺ could significantly improve the luminescent properties of La₂LiTaO₆:Mn⁴⁺. Thus, phosphor La₂LiTaO₆:Mn⁴⁺, Mg²⁺ can serve as a key component to improve color rendering of blue-chip white-LEDs.     

神光-Ⅲ主机黑腔腔形研究与设计

利用三维视角因子软件IRAD3D研究了神光-Ⅲ主机靶丸表面辐射驱动时变对称性和驱动强度随黑腔腔形和排布方式的变化。模拟结果表明:采用椭球形黑腔能显著减小黑腔壁面积从而减小腔壁能量消耗并提高靶丸消耗份额;不同腔形和排布方式下均可通过调节腔长使勒让德不对称性模P2时间积分量较小;采用双环辐照和椭球腔形都利于缩短腔长;四环排布利于调节P4分量,但环向不对称性M4较差;椭球腔双环排布能兼顾极向不对称性P2,P4和环向不对称性M4,且靶丸表面X光驱动强度相对柱腔双环提高25%~27%。     

土壤含盐量与电导率的高光谱反演精度对比研究

探明土壤盐渍化的高光谱遥感监测机理,对改善高光谱遥感监测精度具有重要意义。以南疆地区温宿县、和田县、拜城县的水稻土为研究对象,通过分析土样的高光谱数据和室内测定的盐分与电导率数据,研究了耕作土壤含盐量与电导率的关系,并比较了含盐量和电导率与不同光谱指标的相关性以及二者高光谱反演的精度。结果表明,南疆水稻土的含盐量与电导率的相关性较低,二者之间的关系因地区差异而有较大的变化;含盐量与反射率、一阶微分、连续统去除之间的相关性要优于电导率,特别在一些土壤盐渍化的敏感波段尤为突出;以含盐量建立的多元线性回归、主成分回归、偏最小二乘回归模型的决定系数和相对分析误差均高于电导率。研究表明高光谱信息对土壤含盐量的响应比电导率更敏感,以含盐量为监测指标的高光谱反演精度明显要优于电导率。该结果可为提高土壤盐渍化高光谱遥感监测精度提供理论依据。     

Theoretical investigation of new type of ternary magnesium alloys AMgNi4 (A=Y,La, Ce,Pr and Nd)

New ternary magnesium alloys AMgNi₄ (A=Y, La, Ce, Pr and Nd) have been studied by First-Principles calculations within the generalized gradient approximation. The optimized structural parameters were in good agreement with the available experimental data. The calculated cohesive energies and formation enthalpies showed that these alloys had strong structural stability. Then the elastic constants C_ij of these AMgNi₄ alloys were calculated, and the bulk modulus B, shear modulus G, Young's modulus E, Poisson's ratio ν and anisotropy value A of polycrystalline materials were derived from the elastic constants, the related mechanical properties were further discussed. The electronic structures were also calculated to reveal the underlying mechanism for the structural stability and the elastic property.     

Accurate method for measuring the thermal coefficient of group birefringence of polarization-maintaining fibers

We present a method to accurately measure the group birefringence variation with temperature in high-birefringence polarization-maintaining (PM) fibers using a distributed polarization analyzer. By analyzing polarization cross-talk peaks purposely induced at both ends of a PM fiber, the temperature coefficient of group birefringence can be accurately obtained. We confirm the theoretical prediction that the group birefringence of PANDA and TIGER PM fibers decrease linearly with temperature from -40 °C to 80 °C, and find that the temperature coefficients are -5.93 × 10(-7) °C(-1) and -5.29 × 10(-7) °C(-1) for two types of PANDA fibers, and -5.36 × 10(-7) °C(-1) for a TIGER fiber.     

Leakage current and pyroelectric properties of compositionally graded (Pb,Ca)TiO<Subscript>3</Subscript> films

Highly (100)-oriented, compositionally graded (Pb,Ca)TiO₃ (PCT) thin films with a Ca content from 0 to 24 mol% on Pt/Ti/SiO₂/Si substrates were prepared by a sol-gel process. The graded structure of the Au/PCT/Pt film capacitor showed a well-saturated hysteresis loop at an applied field of 500 kV/cm with remanent polarization (P_r), and coercive electric field (E_c) values of 9.35 C/cm² and 130 kV/cm, respectively. At 100 kHz, the dielectric constant and dielectric loss of the film were 129 and 0.024, respectively. The leakage current density of the graded PCT film was less than 1.0×10^-7 A/cm² over a voltage range from 0 to 4 V. The conduction current depended on the voltage polarity. At low electric field (110 and 180 kV/cm, respectively, for Pt and Au electrodes biased negatively), the Au/PCT and PCT/Pt interfaces form a Schottky barrier. At high electric field (>110 kV/cm), the Au electrode biased negatively shows space-charge-limited current (SCLC) behavior. The temperature dependencies of the pyroelectric coefficients of the graded PCT film were measured by a dynamic technique. From 20 to 82 °C, the pyroelectric coefficients of graded PCT film remain steady in the range 106 to 118 C/m²K. The detectivity figure of merit (F_D) of the graded PCT film was 6.7×10^-6 Pa^-0.5. PACS 77.80.-s; 77.70.+a; 77.22.-d; 51.50.+v; 68.37.-d     

Experiment and dynamic simulations of radiation damping of laser-polarized liquid<Superscript>129</Superscript>Xe at low magnetic field in a flow system

Radiation damping is generally observed when a sample with high spin concentration and high gyromagnetic ratio is placed in a high magnetic field. However, we firstly observed liquid-state¹²⁹Xe radiation damping with laser-enhanced nuclear polarization at low magnetic field in a flow system in which the polarization enhancement factor for the liquid-state¹²⁹Xe was estimated to be 5000, and, furthermore, theoretically simulated the envelopes of the¹²⁹Xe free induction decay and spectral lineshape in the presence of both relaxation and radiation damping with different pulse flip angles and ratios ofT ₂ ^* /T _rd. The radiation damping time constantT _rd of 5 ms was derived on the basis of the simulations. The reasons of depolarization and the further possible improvements were also discussed.     

大学物理实验网络教学平台的建构与应用

利用多媒体开发软件及网页制作工具,建构了一个大学物理实验网络教学平台。介绍了此平台的详细设计方案,以及它所具有的功能和特点,探索大学物理实验多媒体网络辅助教学的新应用。     

Study on the surface erosion route to the fabrication of TiO2 hollow spheres

Three-dimensional (3D) architecture of TiO₂ hollow sphere has many excellent and interesting performances that attract significant attention nowadays. In this paper, a simple surface erosion approach to the fabrication of TiO₂ hollow spheres via the hydrothermal process has been developed. The morphologies and the phase were characterized by scanning electron microscopy (SEM) and X-ray diffractometer (XRD). The results indicate that the anatase-type TiO₂ hollow spheres with a diameter of ∼1 μm are successfully synthesized. The shell thickness of TiO₂ hollow spheres is ∼150 nm and the size of hollow cavity is ∼600 nm. By the control experiments, the influence of ammonium fluoride and hydrogen peroxide on the hollow spherical structures was studied. Hydrogen peroxide acts as both the oxidant and the bubble generator, ammonium fluoride is crucial for the erosion and dissolution of titanium, the detailed dissolution-crystallization mechanism for the formation of TiO₂ hollow spheres was also proposed.