中子辐照α-Al2O3单晶的光学性质研究

本文利用吸收光谱法、光致发光光谱法和拉曼光谱法对中子辐照的α-Al2O3进行研究.吸收光谱表明,中子辐照除产生F2、F2+、F2+2和F3色心外,还能产生[Al-O]3-色心,它对应着325 nm和638 nm两个吸收峰,且具有较低的热稳定性,经300℃退火后消失.光致发光谱法除了检测到F2、F2+和F2+2色心对应的发光峰外,还检测到625nm和657 nm发光峰.625 nm发光峰可能对应着高剂量中子辐照下特有的发光中心.657 nm发光峰是经800℃处理后唯一存在的发光峰,它可能来自于反位铝缺陷(AlO).此外,拉曼光谱显示该剂量的中子辐照不能导致明显的拉曼峰频移和展宽.     

电子辐照对MgAl2O4尖晶石光学性质的影响

本文利用1.7 MeV电子辐照MgAl2O4尖晶石后,通过吸收谱测量表明,被电子辐照的尖晶石可产生大量的F型色心缺陷, 而且电子的辐照剂量明显地影响尖晶石的光谱特性.随着电子辐照剂量增加, F型色心缺陷的浓度增大;椭偏光谱分析得到的光学常数谱随电子辐照剂量的变化而改变.我们对上述现象进行了合理的分析.     

Sr:BaF2晶体电子辐照诱生F型色心及其转型研究

测试和分析了Sr:BaF2晶体电子辐照前后以及辐照着色的样品光致转型过程的吸收谱.研究结果表明,能量为1.5MeV和1.8MeV的电子束对Sr:BaF2晶体的辐照注量达1015～1016cm-2时,诱生F-H对、F心及其与杂质的复合色心.用波长为632.8nm的He-Ne激光照射电子辐照着色的样品,可使F心转型成FA(Sr2+)心;再用钠光(589.0,589.6nm)照射,又可将FA(Sr2+)心部分回转成F心.     

中子辐照6H-SiC晶体中的钉扎效应

分别对两种不同的6H-SiC晶体进行了总通量为5.74×10~(18) n· cm~(-2)、8.2×10~(18) n· cm~(-2)和1.72×10~(19) n· cm~(-2)的不同剂量的中子辐照,利用X射线衍射等手段观测了中子辐照引起的晶体内部损伤.结果表明:两种样品在不同的中子通量辐照下,消除部分原始缺陷的、纯度较高的样品辐照后的内部损伤明显小于纯度较低、内部原始缺陷较多的样品.样品的辐照损伤不仅取决于中子辐照剂量,还取决于其辐照时的成分和结构.晶体的结构缺陷和杂质,作为一种"钉扎",在辐照过程中作用极大,它们导致了晶体的长程缺陷(如位错)的大幅度增加.     

6H-SiC单晶的中子辐照损伤及其退火特性研究

用剂量为1.72×1019 n/cm2和1.67×1020 n/cm2的中子对掺氮6H-SiC单晶进行辐照,利用紫外-可见(UV-Vis)吸收光谱等方法研究了辐照引起的晶格损伤及随退火温度的回复过程.结果表明:中子辐照产生的大量缺陷使SiC的光吸收明显增加;光学带隙能随辐照剂量的增加而降低,这与禁带中引入的局域态缺陷能级有关.光吸收边出现强烈的连续吸收可能归因于辐照产生的不同类型缺陷簇或局部非晶区域的光散射.对两个剂量辐照的样品进行室温到1600℃的等时退火,发现两个剂量辐照产生的晶格损伤所需的退火回复温度不同,但退火回复过程都呈现出以800℃为转折点的两个相同阶段.     

钨酸钡晶体本征点缺陷的模拟计算

本文利用晶格动力学软件GULP模拟计算了钨酸钡晶体的本征点缺陷,首先利用驰豫拟合的方法得到离子之间的相互作用势,利用这些相互作用势计算得到的结果与实验结果吻合得很好,在此基础上计算晶体本征缺陷的生成能,通过对本征点缺陷生成能的分析得到以下结论:钨酸钡晶体内V2+O的数量要大于V2-Ba的数量;钨酸钡晶体内缺陷态主要以V2-Ba-V2+O空位对和F色心形式存在.     

痕量La杂质对CaF2晶体γ辐照诱导色心光谱特性的影响

氟化钙晶体的抗γ射线辐照性能是其在太空应用的关键性能之一。本文报道了痕量La杂质对氟化钙晶体γ辐照诱导色心的影响。主要采用吸收光谱、电子顺磁共振(EPR)等手段对辐照前后存在不同痕量La杂质的氟化钙晶体进行研究。结果表明，辐照后的氟化钙晶体产生多个色心吸收带，且吸收带的吸收系数随辐照剂量和La杂质浓度增加而增加。EPR证实这种吸收带的形成是由氟化钙晶体中F心引起的，而La³⁺的存在影响氟化钙晶体F心的稳定性和光谱位置，本文提出了La³⁺与氟化钙晶体中F心存在的可能机制。     

钼酸镉晶体本征点缺陷的计算机模拟计算

本文利用GULP计算软件拟合了CdMoO4晶体势参数,在此基础上研究了该晶体的本征点缺陷,计算了本征点缺陷的生成能.结果表明,在CdMoO4晶体生长过程中,孤立缺陷主要以肖特基缺陷的形式(Vo2+和Vcd2-)存在.晶体中氧的夫伦克儿缺陷具有较低的生成能,是CdMoO4晶体的主要缺陷类型.Cd的夫伦克儿缺陷在高温条件下将起重要作用,由氧空位引起的F心和F+心与700 nm吸收带的形成有关.     

钼酸钙晶体中点缺陷的计算机模拟

本文根据第一性原理计算了含电子型色心的钼酸钙晶体的电子结构,计算结果表明钼酸钙晶体中F心和F+心不会在可见光范围内引起吸收,而氧空位的存在使钼酸钙晶体呈现蓝色.     

γ辐射及退火MgAl2O4透明陶瓷光谱特性研究

本文用不同剂量的γ射线辐照镁铝尖晶石透明陶瓷,并对辐照后的样品进行等时退火,UV-VIS和FI-IR测试表明,辐照前3360cm-1处有吸收峰,它是由V-1OH心吸收引起的.经γ辐射,样品在370nm处产生吸收带,它是由辐照产生的V型色心吸收引起的.通过退火可以使V型色心吸收带消除.结果表明:较低剂量的γ辐照能降低陶瓷紫外到红外的透过率;大剂量的γ辐照能在陶瓷中产生退火效应,能增加陶瓷红外透过率.     

CsI-LiCl共晶材料的坩埚下降法生长与闪烁性能研究

本文采用坩埚下降法,在真空密封的石英坩埚中成功生长出CsI-LiCl与CsI-LiCl:Na共晶闪烁体。通过扫描电子显微镜(SEM)观察晶体微结构表明该共晶中LiCl相与CsI相存在周期性的层状排列,CsI相的厚度在5 μm左右。共晶样品的X射线激发发射谱显示在CsI-LiCl和CsI-LiCl:Na共晶样品存在缺陷发光,在CsI-LiCl样品中还观察到了纯CsI的自陷激子(STE)发光。CsI-LiCl样品在α粒子激发下的多道能谱中观察到明显的全能峰,这一结果证明CsI-LiCl共晶可用于热中子探测的潜力。     

静电纺丝法制备CeO2微纳米纤维及其除氟性能

以聚丙烯腈(PAN)为载体,六水合硝酸铈[Ce(NO₃)₃·6H₂O]为原料,采用静电纺丝法制备了Ce(NO₃)₃/PAN纤维,在空气中热处理得到CeO₂微纳米纤维,通过XRD、BET和SEM对CeO₂微纳米纤维进行表征。采用静态吸附实验探讨了CeO₂微纳米纤维去除水溶液中氟离子的性能,考察了溶液pH值、初始氟离子浓度及共存阴离子等对吸附性能的影响。结果表明,pH=3时,CeO₂微纳米纤维对F^-的吸附性能最佳,CeO₂吸附量随着F^-浓度的增大呈上升趋势。CeO₂微纳米纤维对F^-的吸附等温线遵循Langmuir模型,二级动力学模型能很好地描述CeO₂微纳米纤维对F^-的吸附过程。CeO₂微纳米纤维的除氟性能优良,可为其实际应用提供理论参考。     

Triethyl ammonium salt of O,O′-bis(p-tolyl)dithiophosphate, [Et3NH]+[(4-MeC6H4O)2PS2]−

Triethyl ammonium Salt of O,O′-bis(p-tolyl)dithiophosphate and O,O′-bis(m-tolyl)dithiophosphate have been obtained by reaction of p- and m-cresol, respectively with P₂S₅ in toluene and have been characterized by elemental analysis, IR, ¹H and ³¹P NMR spectroscopy. The molecular structure of O,O′-bis(p-tolyl)dithiophosphate has been determined. Crystal data: [Et₃NH]⁺[(4-MeC₆H₄O)₂PS₂]⁻: Monoclinic, P2₁/c, a=15.2441(9) ?, b=10.415(2) ?, c=3.9726(9) ?, β=91.709(7)°, V=2217.5(1) ?⁻³, Z=4.Supplementary materials Additional material available from the Cambridge Crystallographic Data Centre (CCDC no. 600927 for [Et₃NH]⁺[(4-MeC₆H₄O)₂PS₂]⁻ comprises the final atomic coordinates for all atoms, thermal parameters, and a complete listing of bond distances and angles. Copies of this information may be obtained free of charge on application to The Director, 12 Union Road, Cambridge CB2 2EZ, UK (fax: +44-1223-336033; email: deposit@ccdc.cam.ac.uk or www:http://www.ccdc.cam.ac.uk).     

Crystal structure of Zn4Na(OH)6SO4Cl·6H2O

The structure of Zn₄Na(OH)₆SO₄Cl·6H₂O, a secondary mineral from Hettstedt, Germany, was determined by single-crystal X-ray diffraction. The crystals are hexagonal,a=8.413(8),c=13.095(24) Å, space group $P\bar 3$ , Z=2. The structure was refined to R=0.0554 and R_w=0.0903 for 970 reflections with I≥3σ(I). The structure can be described as zinc hydroxide layers perpendicular toc, from which sulfates and chlorides extend. The layers are held together by a system of hydrogen bonds involving hexaaquo Na⁺ ions which occupy the interlayer space.     

Synthesis and Crystal Structure of 5-[2-(6-bromonaphthalenyloxymethyl)]-3-(4-morpholinomethyl)-1,3,4-oxadiazole-2(3<Emphasis Type="Italic">H</Emphasis>)-thione

Abstract  The title compound, C₁₈H₁₈BrN₃O₃S, a derivative of 1,3,4-oxadiazole, crystallizes in the triclinic space group P-1 with unit cell parameters a = 6.8731(3), b = 8.9994(4), c = 15.7099(6) ?, α = 92.779(3)°, β = 130.575(3)°, γ = 107.868(4)°, Z = 2. The dihedral angle between the mean planes of the planar naphthyl and morpholine (chair) rings with the planar oxadiazol ring is 50.1(8) and 76.8(6)°, respectively. The planar naphthyl ring is twisted 52.2(5)° with the mean plane of the morpholine ring. A group of four intermolecular close contacts are observed between a bromine atom and hydrogen atoms from the closely packed naphthyl, morpholine and oxy–methyl groups in the unit cell. These molecular interactions in concert with an additional series of π–π stacking interactions that occur between the center of gravity of the two 6-membered rings of the naphthalene group influence the twist angles of each of these three groups. A MOPAC AM1 calculation of the conformation energy of the crystal structure [226.0128(9) kcal] compared to that of the minimum energy structure after geometry optimization [29.9744(1) kcal] reveals a significantly reduced value. The twist angles of the three groups above also change after the AM1 calculation giving support to the influence of both intermolecular C–H···Br short-range interactions and Cg π–π stacking interactions on these angles which therefore play a role in stabilizing crystal packing. Graphical Abstract  Crystal structure of 5-{[(6-bromonaphthalen-2-yl)oxy]methyl}-3-(morpholin-4-ylmethyl)-1,3,4-oxadiazole-2(3H)-thione, C₁₈H₁₈BrN₃O₃S, is reported and its geometric and packing parameters described and compared to a MOPAC computational calculation. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Crystal structure of irisolidone from the flowers of Pueraia lobata

Irisolidone (5,7-dihydroxy-6,4′-dimethoxyisoflavone) was isolated from the flowers of Pueraia lobata and its crystal structure was examined by X-ray single crystal diffraction. The crystal structure of irisolidone is monoclinic, space group P2₁/c with a = 15.491(9) ?, b = 7.895(4) ?, c = 13.321(7) ?, β = 110.546(9)° and Z = 4. Hydrogen bonding and aromatic π–π stacking assemble the title compound into a three-dimensional networking structure.     

X-ray analysis of sideroxol from <Emphasis Type="Italic">Sideritis leptoclada</Emphasis>

Sideroxol (1), a kaurane diterpene which has the ent-7α,18-dihydroxy-15β,16β-epoxykaurane structure (MW = 320.47, C₂₀H₃₂O₃) was obtained from the acetone extract of Sideritis leptoclada plant as well as from some other Sideritis species. It crystallizes in the orthorhombic space group P2₁, 2₁, 2₁ with a = 10.967(3), b = 24.555(5), c = 6.372(4) Å, Dc = 1.240 g cm⁻³, Z = 4, and refines to R = 0.065 for 721 independent reflections. The skeleton consists of three fused six-membered rings and a five-membered ring with fused epoxide. The six membered rings exhibited slightly distorted chair conformation. In addition to sideroxol, two kaurane and five kaurene diterpenes were isolated from the hexane and acetone extracts of the studied plant.     

New zeotype borophosphates with chiral tetrahedral topology: (H)0.5M1.25(H2O)1.5[BP2O8]·H2O (M = Co(II) and Mn(II))

Two new isostructural open‐framework zeotype transition metal borophosphate compounds, (H)_0.5M_1.25(H₂O)_1.5[BP₂O₈]·H₂O (M = Co(II) and Mn(II)) were synthesized by mild hydrothermal method. The structure of compounds were characterized by single‐crystal X‐ray diffraction which have ordered, alternating, vertex‐sharing BO₄, PO₄, and (MO₄)OM(H₂O)₂ groups with hexagonal, P 6₁ 2 2 (No 178) space group and unit cell parameters for Co a = 9.4960(6) Å, c = 15.6230(13) Å, for Mn a = 9.6547(12) Å, c = 15.791(3) Å, Z = 1 for both of them. TGA/DTA analysis, IR spectroscopy were used for characterization. Magnetic susceptibility measurements for both of the compound indicate strong antiferromagnetic interaction between metal centers. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Photoluminescence characteristics of Mg- and Si-doped GaN thin films grown by MOCVD technique

We have studied the optical, structural and surface morphology of doped and undoped GaN thin films. The p- and n-type thin films have been successfully prepared by low-pressure MOCVD technique by doping with Mg and Si, respectively. The different carrier concentrations were obtained in the GaN thin films by varying dopant concentrations. Photoluminescence (PL) studies were carried to find the defect levels in the doped and undoped GaN thin films at low temperature. In the undoped GaN thin films, a low intensity and broad yellow band peak was observed. The donor–acceptor pair (DAP) emission and its phonon replicas were observed in both the Si or Mg lightly doped GaN thin films. The dominance of the blue and the yellow emissions increased in the PL spectra, as the carrier concentration was increased. The XRD and SEM analyses were employed to study the structural and surface morphology of the films, respectively. Both the doped and the undoped films exhibited hexagonal structure and polycrystalline nature. Mg-doped GaN thin films showed columnar structure whereas Si-doped films exhibited spherical shape grains.     

Solubility of Ag2O into the Na2O–B2O3–Al2O3 system

The solubility of Ag₂O was measured for the Na₂O–B₂O₃ and Na₂O–B₂O₃–Al₂O₃ system with the rotating crucible method and static method, respectively, under air atmosphere at temperatures ranging from 1273 to 1423 K. The contamination of melts from crucibles could be avoided by the rotating crucible method, with which it became possible to measure the solubility of Ag₂O for the Na₂O–B₂O₃ system above the melting point of Ag for the first time. It was found that the addition of Na₂O decreases the solubility of Ag₂O while the addition of Al₂O₃ had little effect on the solubility. The effect of Na₂O and Al₂O₃ on the solubility of Ag₂O is expressed by interaction coefficients and is analyzed in terms of the basicity of melts. The solubility of Ag₂O in Na₂O–B₂O₃–Al₂O₃ melts increased with increased temperature. This phenomena was explained by a small enthalpy change in oxidation of silver.