Ba2+,Al3+,Sr2+掺杂YF3∶Ho3+,Yb3+上转换发光的研究

为了提高上转换材料在激光防伪领域的绿光发射强度,采用高温固相法制备Ba2、Al3+、Sr2+掺杂YF3∶Ho3+,Yb3+材料.通过980 nm近红外激发的上转换发射光谱,可知Ba2+、Al3+、Sr2+的掺杂都会使得晶格收缩,降低稀土离子周围晶体场的对称性,其546 nm绿光强度分别是未掺杂该金属离子样品的1.6倍、1.1倍、1.2倍.并根据X射线衍射(XRD)探究Ba2+含量对晶相的作用.通过差热分析(DTA)、上转换发射光谱、XRD、扫描电子显微镜(SEM),结果表明:对于最佳Ba2、Al3+、Sr2+掺杂含量但不同烧结温度的样品,当合成温度为940℃时发光性能、结晶度和晶粒生长较好.通过发射强度与激发电流的拟合结果,说明546 nm绿光是双光子吸收过程,并阐述980 nm激发YF3∶Ho3+,Yb3发光材料的能级跃迁过程.     

La2Ca1-xSrxB10O19(Sr2+∶LCB)晶体的生长及光学性质

通过顶部籽晶法生长出掺5;和8;Sr2+的La2CaB10O19(LCB)晶体,ICP测得LCB晶体中Sr2+掺入量分别为1.75;和2.02;.XRD证实Sr2+的掺入对LCB晶体晶胞参数的影响较小.摇摆曲线测得Sr2+∶LCB晶体半高宽为36",表明晶体具有较高质量.Sr2+∶LCB晶体在300～2000 nm波段具有较高的透过率,紫外截止边为172 nm.拟合的色散方程符合Sr2+∶LCB晶体折射率的实验值,理论计算表明Sr2+∶LCB晶体可实现相位匹配,其最短二倍频波长小于LCB晶体.     

电解液浓度对BaxSr(1-x)TiO3微弧氧化膜微观结构及介电性能的影响

用Ba(OH)2·8H2O和Sr(OH)2·8H2O配制电解液,工艺参数分别设置为电流密度20 A/dm2、电流频率100Hz、反应时间20 min及占空比85;,采用微弧氧化法在工业纯Ti板(99.5;)表面原位生长BaxSr(1-x)TiO3薄膜.分析了相同Ba2+ /Sr+比条件下,电解液浓度对薄膜物相、表面形貌及薄膜厚度的影响.结果表明:所得薄膜均主要由四方相Ba0.5Sr0.5TiO3构成;Ba2+和Sr2+各为0.2 mol/L时所得薄膜的表面平整度及致密性最好,表面粗糙度值最小,并检测了该薄膜在不同频率下的介电常数和介电损耗,发现两者均随频率的增加而减小;薄膜厚度随电解液浓度的增加而增加.     

光学浮区法制备Ba1-xSrxTiO3晶体

采用光学浮区法生长了尺寸为(6～8)mm×(40～ 80)mm的Ba1-xSrxTiO3晶体(x=0、0.01、0.016、0.02),并对其生长温度、旋转速度、生长速度等生长工艺参数进行了研究.实验过程中固液面稳定,X射线双晶摇摆曲线显示样品具有较好的晶体质量.XRD测试显示Sr2+的掺入能够抑制BaTiO3六方相的生成,BaTiO3四方相衍射峰向高衍射角方向移动.各组分晶体样品红外透过率超过80;.拉曼光谱显示存在峰值为489～496 cm-1的峰,这可以被认为是三方相的存在证据,这一变化应该为Sr2+的掺入所导致的.     

Yb3+: Sr3Gd(BO3)3激光晶体的生长和光谱特性

采用提拉法(Czochralski)生长出了掺Yb3+的Sr3Gd(BO3)3晶体,晶体尺寸达到:25 mm×30 mm.测量了Yb3+: Sr3Gd(BO3)3晶体的吸收谱、荧光谱以及荧光寿命.Yb3+: Sr3Gd(BO3)3晶体在975 nm有一半峰宽为7 nm的强吸收峰,π谱的吸收跃迁截面σa=7.28×10-21 cm2,在1040 nm的发射跃迁截面σe=1.43×10-21 cm2.辐射寿命为1.46 ms, Yb3+浓度为13 at;时的荧光寿命f=2.14 ms,Yb3+浓度为0.5 at;时的荧光寿命f=1.21 ms.     

Ba3(VO4)2晶体的生长和拉曼性质的研究

采用提拉法生长了尺寸为φ22mm×50 mm的Ba3(VO4):晶体.室温下测试了Ba3(VO4)2晶体不同激发配置下自发拉曼散射光谱.另外测试了该晶体在532 nm、25 ps脉冲下的受激拉曼散射,观察到3阶斯托克斯线(625.5 am)和1阶反斯托克斯线(506.8 nm),并估算了Ba3(VO4)2晶体的稳态拉曼增益系数.     

双掺Er~(3+)/Yb~(3+)∶Sr_3La_2(BO_3)_4晶体的生长与光谱特性

采用提拉法生长了尺寸为20mm×30mm的Er3+/Yb3+∶Sr3La2(BO3)4晶体,研究了Er3+/Yb3+∶Sr3La2(BO3)4晶体的吸收光谱和荧光光谱。根据Judd-Ofelt理论分析并计算了辐射跃迁几率、辐射寿命、荧光分支比等光谱参数,获得的唯象参数为:Ω2=15.59×10-20cm2,Ω4=2.25×10-20cm2,Ω6=1.49×10-20cm2。在Er3+/Yb3+∶Sr3La2(BO3)4晶体中Er3+在1533nm处发射跃迁截面为7.88×10-21cm2,Er3+的4I13/2→4I15/2能级跃迁的荧光寿命和辐射寿命分别为0.728ms和4.24ms,结果表明Yb3+对Er3+有敏化作用,提高了对泵浦光的吸收能力,Er3+/Yb3+∶Sr3La2(BO3)4晶体可望作为1.55μm波段的一种有潜力的激光材料。     

Ba7(BO3)3F5晶体结构及热分析

采用高温溶液法从BaCO3,BaF2及H3BO3混合体系中生长出了一种氟硼酸钡晶体,Ba7(BO3)3F5晶体属六方晶系,空间群为P63mc,晶胞参数:a=1.11562(15) nm,c=0.72415(14) nm,Z=2,V=0.7805(2) nm3.Ba7(BO3)3F5晶体结构是由Ba(1)O7F3基团,Ba(2)O4F3基团,Ba(3)O6F4基团和独立的BO3基团相互连接形成的三维空间网络结构.Ba7(BO3)3F5的热分析分析结果表明Ba7(BO3)3F5在1070℃同成份熔化.     

Eu3+掺杂SrZn2(PO4)2晶体的发光光谱和结构研究

采用高温固相合成法合成了Eu3+掺杂的SrZn2(PO4)2晶体,使用X射线粉末衍射(XRD)、扫瞄电子显微镜(SEM)、傅立叶红外光谱(FT-IR)等手段对晶体结构进行了表征.使用了激光选择激发和发射技术,对于Eu3+掺杂的SrZn2(PO4)2晶体进行了发光表征和研究,分别测试了Eu3+离子的5D0→7F0激发光谱和5D0→7FJ (J = 1, 2, 3, 4)发射光谱、发光衰减及荧光寿命.Eu3+的7F0和5D0态都是单态,不发生分裂,对应于7F0→5D0激发跃迁的数目就是Eu3+在晶格中的晶体学位置.实验证实了在Eu3+掺杂的SrZn2(PO4)2晶体之中,Eu3+在样品中只有一个晶体学位置,Eu3+取代了与它半径相近的Sr2+而处于较高的对称格位.     

共生晶体Mn2Hg4(SCN)12和MnHg(SCN)4的形成

采用恒温蒸发法从水溶液中生长Hg2+、Mn2+为双配位中心的SCN- 的配合物晶体.生长液中Hg2+含量较SCN-适当过量的条件下,出现Mn2Hg4(SCN)12晶体和MnHg(SCN)4晶体共生现象.MnHg (SCN)4晶体中Hg2+只与SCN-配位,Mn2+只与NCS-配位,而Mn2Hg4(SCN)12晶体中部分Hg2+可以同时与SCN-和NCS-配位体结合,并且部分SCN-同时和2个Hg2+结合成桥式结构.Mn2Hg4(SCN)12晶体中Mn2+的配位数由MnHg(SCN)4晶体中的4配位增大为5配位和6配位.Mn(NCS)4-6 和Mn(NCS)3-5 配位多面体的存在使Mn2Hg4(SCN)12晶体的颜色比MnHg(SCN)4晶体的颜色浅.     

Processes in phase boundary region during liquid phase growth

The behavior of components within the phase boundary region during liquid phase growth is the subject of the present article. Based on the supposition that the phase boundary is a structured region, repeating the periodicity of the substrate, the distribution of different components within the phase boundary is considered. Assuming that the value of the supersaturation at the upper end of the phase boundary defines the growth rate of the compound, a relation has been derived, concerning the extension of the phase boundary. The case of liquid phase epitaxial growth of GaAs is considered and an effort for evaluation of the phase boundary extension is undertaken. The linear dependence of the stationary growth rate on the cooling rate, predicted previously, is proved experimentally.     

The Lyotropic Smectic Phase on the Flory Lattice

Abstract

The Flory lattice approach for rod-like molecules is extended to encompass the position-restricted (smectic-A) phase. The phase equilibria conditions are obtained from equity of relevant chemical potentials, together with minimization conditions of the Gibbs potential with respect to the system orientational (Flory disorder index, y) and positional (translational disorder index, ζ in the smectic phase) order.     

Notes on some supposed transitions of the phase NiBi

X‐Ray, DSC and magnetic susceptibility measurements were performed with NiBi specimens in the interval from room temperature to 700 K. The hypothesis of solid‐state transitions in this phase was not confirmed. Thermal and magnetic effects are observed, but they are due to the existence of small amount of phases others than NiBi (i.e. unreacted Ni and Bi). (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Investigation of the structure and mechanisms of thermal motion in nanostructured undecylenic acid

Abstract

We have compared the structure, phase transitions and the thermal motion mechanisms of the undecylenic acid in bulk and inside a porous matrix using powder X-ray diffraction, calorimetry and IR-spectroscopy methods. The matrix used was a porous silicon with cylindrical pores (D?=?20?nm). The interaction between the walls of the porous silicon and the nanocrystals of the undecylenic acid results in a crystalline structure, which is significantly different from the structure of bulk undecylenic acid. A phase transition in the wall-adjacent layer of the undecylenic acid nanocrystals was shown to take place. The solid-state phase transition temperatures, as well as the melting point, were shown to be lower for nanocrystals. Topological soliton motion mechanism was suggested to explain the thermal motion of the undecylenic acid molecules in the rotator phase.     

Studies of Image Processing and Refractive Index in Blue Phase

The isotropic - blue phases - cholesteric phase transitions are studied in a thermotropic (COC) by image processing and refractive index measurements. Textures of blue phases are optically characterized as well as their transition points. The experimental investigation employed here is sensitive to detect changes in the structural configuration of blue phases as a consequence of our refractive index data. In this context the experimental results are presented and discussed.     

Crystallization and stability of different protein crystal modifications: A case study of lysozyme

The crystallization, including both the phase diagram and the phase transition of hen egg white lysozyme (HEWL) was investigated. A tetragonal modification and a needle modification were obtained during crystallization. The phase diagram and stability of two modifications in both acid and basic pH solutions (pH 4.5, 8.0 and 9.0) were determined. Besides in acid solutions, the well‐known tetragonal crystals can also be obtained in basic solutions at low temperature (7 °C) while the needle like modification can only crystallize in a basic solution. Based on the phase diagram, phase transfer behavior was found to exist between the two modifications. In basic solutions, tetragonal modification can transfer to needle shaped crystals. This process can be affected by a changing of pH and temperature. While in acid buffer, the needle shaped crystals dissolve and tetragonal crystals crystallize and remain in solution.     

Microstructure and phase transformation of Ti3AC2 (A = Al,Si) in hydrofluoric acid solution

In this paper, Ti₃AC₂ (A = Al, Si) were prepared by pressureless argon shielding synthesis technique. The microstructure and phase transformation of as‐prepared Ti₃AC₂ (A = Al, Si) in hydrothermal hydrofluoric acid (HF) solution were investigated systematically. Results showed that the obtained Ti₃AlC₂ and Ti₃SiC₂ were closely aligned layered structure. In hydrothermal HF solution, Al or Si element was preferentially etched from the layered structure, inducing obvious transformation of microstructure and phase composition. For Ti₃AlC₂, Al atoms diffused out of the structure and reacted with HF to form AlF₃•H₂O, which induced the rearrangement of the Ti and C atoms, and finally resulted in the formation of TiC_x cubic phase. With the hydrothermal temperature and reaction time increasing, the TiC_x phase gradually disappeared and the grain size of AlF₃•H₂O gradually increased. When Ti₃SiC₂ was immersed in hydrothermal HF solution, the main products were TiC and SiC. Interestingly, with the hydrothermal treatment temperature and reaction time increasing, TiC gradually disappeared, while SiC nearly kept unchanged. This can be explained that SiC was covalently bonded carbide, while TiC was metallically bonded, having relatively weak bond energy and consequently being unstable in hydrothermal HF solution.     

相变存储器及其用于神经形态计算的研究综述

目前随着人工智能领域的兴起以及人们对数据存储和计算的强烈需求,迫切需要存储器的改进和类似于人脑的高效存储运算效率。所以,相变存储器及其用于神经形态计算的研究是极具价值的。相变存储材料(PCMs)受到激发时所产生的电阻值变化可以用来建立尖峰神经网络从而实现模拟神经形态计算系统。本文介绍了相变存储器物理机制,其中包括相变材料的相变原理及主要性能特征,重点叙述了相变存储器在优化存储与计算方向的研究进展和应用,进而为该领域未来的发展方向提供参考。     

Phase transition and thermal stability of reentrant smectic phase in mixture of liquid crystalline materials

In the present work, our investigation is to study the optical and thermal properties of the binary mixture of cholesteric and nematic compounds namely, decyloxy benzoic acid (DBA), and cholesteryl chloride (ChCl), which exhibits different liquid crystalline phases with reentrant smectic-A phase. The reentrant smectic-A phase has been observed at different concentrations and at different temperatures. The existence of reentrant smectic-A phase has been observed by optical microscopic studies. The temperature variation of optical anisotropy, X-ray and helical pitch of the cholesteric (N^*) phase has also been discussed.     

高纯TiO2超微粉体的制备

以廉价的TiCl4为原料,液体石蜡为纯化剂,氨水作形核剂,制备出高纯TiO2超微粉体。用XRF分析了样品的物相组成;XRD和SEM等手段表征了粉体合成过程的物相变化和形貌特征。结果表明,TiCl4经过矿物油(液体石蜡)除钒和精馏除铁等杂质后进行水解,当TiCl4溶液浓度0.65 mol/L,水解温度60℃、反应时间2 h、pH值=7、在800℃煅烧2 h条件下,制备出TiO2的纯度达到99.9952%,晶型为金红石相,晶粒尺寸约0.65μm,形貌近球形。