Y3+/Li+和Y3+/Na+双掺杂氟化钡快响应闪烁晶体

氟化钡(BaF₂)晶体是已知响应最快的闪烁晶体,在高能物理、核物理及核医学等领域有着广泛的应用前景。抑制BaF₂晶体的慢发光成分对其工程应用至关重要。本文利用坩埚下降法制备了高Y³⁺掺杂浓度5%、8%、10%(摩尔分数)的BaF₂晶体,并采用Y³⁺与碱金属离子(Li⁺、Na⁺)共掺杂的方法形成电荷补偿阻止间隙F^-的产生,制备了双掺杂型BaF₂快响应闪烁晶体,进而基于优化的5 ns和2 500 ns时间门宽测试方法,研究了Y³⁺掺杂浓度以及Y³⁺与碱金属离子(Li⁺、Na⁺)共掺杂浓度对BaF₂闪烁晶体快/慢成分比的影响规律。结果表明,生长的高浓度Y³⁺掺杂BaF₂晶体的光学质量优异,在220 nm和300 nm处透过率分别高于90%和92%;随着Y³⁺掺杂浓度由0提高至10%,BaF₂晶体的慢发光成分显著降低,快/慢成分比由0.15提高至1.21;生长的Y³⁺/Li⁺及Y³⁺/Na⁺共掺杂BaF₂晶体的慢发光成分较Y³⁺掺杂BaF₂晶体进一步降低,快/慢成分比最高分别可达1.63和1.61。研制的双掺杂BaF₂快响应闪烁晶体有望应用于高能物理、核物理前沿实验等重要领域。     

氟磷共掺杂二氧化硅光纤预制棒的表面晶化

对F、P共掺杂光纤预制棒退火后的表面晶化行为进行了研究.由改进的化学汽相沉淀法制备的氟和磷共掺杂二氧化硅光纤预制棒玻璃样品在6 h的1 150 ℃控温加热处理后,其表面发生晶化.用X-射线衍射仪观测其晶相,主要为α-方石英,可使玻璃具有二阶光学非线性;用光学显微镜观察了其表面形貌并对结晶微粒的大小进行测量,知晶粒大小在十几到几十μm之间,会造成散射损耗的增加.实验结果,还显示氟对结晶过程有很大的影响.     

Temperature characteristics of small signal gain for Nd/Cr:YAG ceramic lasers

Thermal dependence on the small signal gain of Nd/Cr:YAG (yttrium aluminum garnet) ceramics was observed experimentally. Usually, Nd:YAG crystal and ceramics have remarkable gain reduction when optical pumping is performed and the temperature of the laser media is upped to 373 K. A CW laser light generated in a 1064 nm Nd:YAG laser oscillator was amplified by Nd/Cr:YAG ceramic amplifier, and the output power was measured at non-saturation level. Laser small signal gain of the ceramic disk was kept to 470 K. This property was remarkably different from one of Nd:YAG crystals or ceramics. The peak shift of the fluorescence was observed experimentally when the temperature is high.     

High repetition rate laser pulses amplified by Nd/Cr:YAG ceramic amplifier under CW arc-lamp-light pumping

Laser pulses with high repetitive rate generated from a Q-switch microchip Nd:YAG oscillator were amplified by Active mirror composed of Nd/Cr:YAG ceramic pumped by CW arc-lamp. The laser pulses were amplified, and saturation of averaged output laser power was observed. Repetitive ratio of injected laser pulses was changed from 20 to 100 kHz. Averaged output laser power and gain were measured, and gain coefficient and power-extraction efficiency were evaluated. Output laser power was calculated and compared to experimentally measured one, and the calculated results are consistent with the experimental ones. For amplification of laser pulses with high repetitive ratio, this laser material can realize very high laser gain with low pumping power density and high optical-optical conversion efficiency under CW-lamp-light pumping.     

Sm~(3+),Sr~(2+)共掺杂对CeO_2基电解质性能影响的密度泛函理论+U计算

Sm~(3+),Sr~(2+)共掺杂CeO_2的离子电导率被证实可高达Sm~(3+)掺杂CeO_2离子电导率的近两倍,然而,共掺杂对CeO_2电导率的作用机理尚不明确.本文利用第一性原理计算的密度泛函理论+U方法,对Sm~(3+)和Sr~(2+)共掺杂的CeO_2进行了系统的研究,对比Sm~(3+)或Sr~(2+)单掺杂的CeO_2体系,计算并分析了共掺杂体系的电子态密度、能带结构、氧空位形成能以及氧空位迁移能等微观属性.计算结果表明,Sm~(3+),Sr~(2+)的共掺杂对CeO_2基电解质性能的提高具有协同效应,二者的共掺杂不仅能协同抑制CeO_2体系的电子电导率,还能在单掺杂CeO_2的基础上进一步降低氧空位形成能,Sm~(3+)的存在还有助于降低Sr~(2+)对氧空位的俘获作用,而Sr~(2+)的加入则能够在Sm~(3+)掺杂CeO_2的基础上进一步降低最低氧空位迁移能,爬坡式弹性能带方法计算表明共掺杂体系的氧空位迁移能最低可达0.314/0.295 eV,低于Sm~(3+)掺杂CeO_2的最低氧空位迁移能.研究揭示了Sm~(3+),Sr~(2+)共掺杂对CeO_2电导率的协同作用机理,对进一步研发其他高性能的共掺杂电解质材料具有重要的指导意义.     

A brief review of co-doping

Dopants and defects are important in semiconductor and magnetic devices. Strategies for controlling doping and defects have been the focus of semiconductor physics research during the past decades and remain critical even today. Co-doping is a promising strategy that can be used for effectively tuning the dopant populations, electronic properties, and magnetic properties. It can enhance the solubility of dopants and improve the stability of desired defects. During the past 20 years, significant experimental and theoretical efforts have been devoted to studying the characteristics of co-doping. In this article, we first review the historical development of co-doping. Then, we review a variety of research performed on co-doping, based on the compensating nature of co-dopants. Finally, we review the effects of contamination and surfactants that can explain the general mechanisms of co-doping.     

沉积温度对钛硅共掺杂类金刚石薄膜生长、结构和力学性能的影响

采用中频磁控溅射Ti80Si20复合靶在单晶硅表面制备了共掺杂的类金刚石薄膜.研究了沉积温度对薄膜生长速率、化学成分、结构、表面性质和力学性能的影响.结果表明:随沉积温度升高,薄膜生长速率降低,薄膜Ti和Si原子浓度增加,C原子浓度降低;在高温下沉积的薄膜具有低sp3C含量、低表面接触角、低内应力和高的硬度与弹性模量.基于亚表层注入生长模型分析了沉积温度对薄膜生长和键合结构的影响,从薄膜生长机制和微观结构解释了表面性质和力学性能的变化.     

硫和银共掺杂介孔TiO2的制备、表征及其对染料的光催化降解活性

以P123为模板,以钛酸四正丁酯、硝酸银和硫脲为原料采用模板法制备了一系列硫和银共掺杂介孔TiO₂光催化材料．利用SEM、XRD、BET和紫外-可见光谱等技术对其形貌、晶体结构及表面结构、光吸收特性等进行了表征．以甲基橙溶液的光催化降解为模型反应,考察了不同掺杂量的样品在紫外和可见光下的光催化性能．结果表明,用模板法制备的共掺杂介孔TiO₂光催化材料在紫外和可见光条件下较纯介孔TiO₂和单掺杂介孔TiO₂对甲基橙溶液具有更好的光催化降解效果, 且硫和银的掺杂量及样品焙烧温度显著影响该材料的催化性能．当硫掺杂量为2mol%和银掺杂量为1mol%,在500 oC 焙烧2 h所得光催化材料的催化性能最佳,4 h即可使甲基橙的降解率达98.8%,重复使用4次仍可使甲基橙的降解率保持在87.5%以上     

Investigation of structural and optical properties of ZnO films co-doped with fluorine and indium

Undoped ZnO film and ZnO films, which are co-doped with F and In (FIZO) at different concentrations, were synthesized by sol–gel technique and the effects of co-doping of F and In on structural and optical properties of ZnO thin films were investigated. The concentration ratio of [F]/[Zn] was altered from 0.25 to 1.75 with 0.50 step at.% mole and [In]/[Zn] was altered from 0.25 to 1.00 with 0.25 step at.% mole. X-ray diffraction analysis indicates that the films have polycrystalline nature and the (0 0 2) preferred orientation is the stronger peak. No extra phases involving zinc, fluorine and indium compounds were observed even at high F and In content. The grain size of undoped ZnO and FIZO thin films varied between 15 and 20 nm with a small fluctuation. From the SEM images, although the undoped ZnO had a smooth and particle-shaped surface, FIZO films had nanofiber-networks shapes over the surface with average size of 500 nm. The surface morphologies and crystallite sizes for the F and In doped films were slightly different from than those of undoped film. From the optical study, a slight shrinkage of band gap was backwardly observed from 3.36 to 3.25 eV with the increasing of F and In content.     

DFT study on electronic structure and optical properties of N-doped,S-doped,and N/S co-doped SrTiO3

The electronic structures and optical properties of N-doped, S-doped and N/S co-doped SrTiO₃ have been investigated on the basis of density functional theory (DFT) calculations. Through band structure calculation, the top of the valence band is made up of the O 2p states for the pure SrTiO₃. When N and S atoms were introduced into SrTiO₃ lattice at O site, the electronic structure analysis shows that the doping of N and S atoms could substantially lower the band gap of SrTiO₃ by the presence of an impurity state of N 2p on the upper edge of the valence band and S 2p states hybrid with O 2p states, respectively. When the N/S co-doped, the energy gap has further narrowing compared with only N or S doped SrTiO₃. The calculations of optical properties also indicate a high photo response for visible light for N/S co-doped SrTiO₃. Besides, we find a new impurity state which separates from the O 2p states could improve the photocatalytic efficiency and we also propose a model for light electron-hole transportation which can explain the experiment results well. All these conclusions are in agreement with the recent experimental results.