La1．6（MoO4）3∶Eu3＋0．4纳米晶合成及发光特性

采用燃烧法合成了La1．6（MoO4）3∶Eu3＋0．4纳米晶末,研究了其声子-掺杂-晶格相互作用和发光性质。 X射线粉末衍射（XRD）分析表明,在500～900℃退火后,La1．6（MoO4）3∶Eu3＋0．4样品为单一晶相。对样品进行了光致发光（PL）测量,激发Mo6＋-O2－电荷迁移带,观察到Eu3＋的系列发光,表明Mo6＋-O2－带和Eu3＋间存在能量传递,中心波长分别在λ1＝469 nm和λ2＝426 nm处的两个one-phonon边带,相应的声子能量分别为767和1202 cm－1,分别对应于Mo O和Mo—O—Mo伸缩振动。同时,计算了两个局域模电子-声子耦合强度的黄昆因子分别为S1＝0.055和S2＝0.037,为揭示其三价离子高传导特性及其负热膨胀物理特性提供了实验基础。     

非等电子Sb替换Cu和Te后黄铜矿结构半导体Cu_3Ga_5Te_9的热电性能

热电材料是一类能够实现热与电相互转换的功能材料,在制冷和发电领域极具应用潜力.本文采用金属Sb元素非等电子替换Cu3Ga5Te9化学式中的Cu和Te,观察到材料Seebeck系数和电导率提升的现象.这些电学性能的改善与载流子浓度和有效质量的增大及迁移率基本维持不变有关.载流子浓度的提高是由于Sb原子占位在Te晶格位置后费米能级进入到价带所产生的空穴掺杂效应所致,同时也与Cu含量减少后铜空位(V-1Cu)浓度增大相关联.另外,非等电子替换后,阴离子(Te2-)移位导致了晶格结构缺陷参数u和η的改变,其改变量fiu和fiη与材料晶格热导率(κL)的变化密切相关.在766 K时,适量的Sb替换量使材料的最大热电优值(ZT)达到0.6,比Cu3Ga5Te9提高了近25%.因此,通过选择替换元素、被替换元素及替换量有效地调控了材料的电学及热学性能,在黄铜矿结构半导体中实现了非等电子元素替换改善热电性能的思想.     

绿泥石矿物成分与光谱特征关系研究

绿泥石矿物广泛发育于各种岩石和地质环境中,其化学成分的变化,可反映出其形成时的物理化学条件及其光谱特征的变化。为了探索矿物光谱特征与其矿物化学成分间的内在关联性,为利用高光谱技术探测矿物微观信息提供基础依据。通过薄片显微分析,鉴定了岩石样品中的矿物种类及矿物组合特征,圈定出典型的绿泥石矿物颗粒和划分了绿泥石的产状特征;并利用现代电子探针微区分析技术,测定了16件岩石样品中共146个具有典型代表性的绿泥石矿物颗粒的化学成分,据此计算了其n(AlⅣ),n(AlⅥ),n(Fe),n(Mg)与Fe/(Fe+Mg)比值等相关化学参数;此外对测量的岩矿光谱进行分析,提取了岩石样品中绿泥石矿物的特征光谱参量。在以上基础上,对绿泥石矿物的光谱特征参量和其主要晶体化学参数的关系进行分析研究,研究表明绿泥石矿物的诊断性特征吸收波长位置随绿泥石中Fe离子含量的增加而向长波方向移动。研究结果对于利用高光谱遥感技术进行蚀变矿物及造岩矿物种类、成分及结构特征的识别和探测具有重要的指导意义。     

深圳城市气溶胶物理光学特性的观测研究

气溶胶是影响气候变化和空气污染的重要因子.在深圳地区展开气溶胶观测实验,可以获得可靠的光学物理特征,进而有助于准确评估气溶胶在新型超极城市区域的气像和环境效应.本文利用2010年12月至2011年8月太阳光度计、黑碳和浊度计等气溶胶观测资料,分析了新型超级城市深圳地区的气溶胶物理光学特性.深圳地区气溶胶呈明显季节变化,冬、春季由于城市污染性气溶胶的影响,气溶胶光学厚度和Angstrom波长指数都较大,夏季受海盐气溶胶的影响,光学厚度较小,Angstrom波长指数也较小.光学厚度与Angstrom 波长指数对比表明城市综合性污染是引起深圳气溶胶高光学厚度的主要原因.深圳地区气溶胶的散射系数、吸收系数的平均值(标准偏差)分别为178.7×10^-6 m^-1(126.6×10^-6 m^-1)和32.5×10^-6 m^-1(18.1×10^-6 m^-1),均低于珠三角腹地多年观测平均值的二分之一和国内其他大型城市观测值.而单次散射反照率为0.81,与珠三角其他地区得到的结果接近.此外,气溶胶吸收、散射和单次散射反照率呈明显日变化,可能主要受大气边界层变化的影响.     

Comparative study of electrochemical capacitance of multi-walled carbon nanotubes before and after chopping

In the work, short multi-walled carbon nanotubes (S-CNTs) were synthesized by chopping conventional μm-long multi-walled carbon nanotubes (L-CNTs) under ultrasonication in H₂SO₄/HNO₃ mixed acids. A comparative electrochemical investigation performed in 6 M KOH solution demonstrated that a specific capacitance (SC) of ca. 14.6 μF cm⁻² was delivered by the S-CNTs with the specific surface area (SSA) of 207 m² g⁻¹, much larger than that of ca. 10.1 μF cm⁻² for the L-CNTs with the SSA of 223 m² g⁻¹, the reason for which was that S-CNTs with two open ends, due to good ion penetrability, provided more entrances for electrolyte ions to access the inner surface easily through their shorter inner pathway so as to enhance their SSA utilization and geometric SC. The surface structure disruption of S-CNTs, owing to ultrasonication and oxidation during chopping process, deteriorated their electronic conductivity and resulted in an inferior power property in contrast to L-CNTs.     

Synthesis and characterization of Ni-Zn ferrite nanoparticles

Nickel zinc ferrite nanoparticles Ni_xZn_1−xFe₂O₄ (x=0.1, 0.3, 0.5) have been synthesized by a chemical co-precipitation method. The samples were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, electron paramagnetic resonance, dc magnetization and ac susceptibility measurements. The X-ray diffraction patterns confirm the synthesis of single crystalline Ni_xZn_1−xFe₂O₄ nanoparticles. The lattice parameter decreases with increase in Ni content resulting in a reduction in lattice strain. Similarly crystallite size increases with the concentration of Ni. The magnetic measurements show the superparamagnetic nature of the samples for x=0.1 and 0.3 whereas for x=0.5 the material is ferromagnetic. The saturation magnetization is 23.95 emu/g and increases with increase in Ni content. The superparamagnetic nature of the samples is supported by the EPR and ac susceptibility measurement studies. The blocking temperature increases with Ni concentration. The increase in blocking temperature is explained by the redistribution of the cations on tetrahedral (A) and octahedral (B) sites.     

Preparation and investigation of magnetic properties of MnNiTi-substituted strontium hexaferrite nanoparticles

A series of M-type strontium hexaferrite powders with substitution of Mn²⁺, Ni²⁺ and Ti⁴⁺ ions for Fe³⁺ ions according to the formula SrFe₉(Mn_0.5−xNi_xTi_0.5)₃O₁₉, where x ranges from 0 to 0.5 with a step of 0.1, has been prepared via the conventional ceramic method. In order to get nanoparticles, the obtained powders were milled in a high energy SPEX mill for 1 h. XRD investigations of the unmilled and milled powders show that the prepared samples are all single phase hexaferrite. Lattice parameters and mean crystallite sizes of the powders were determined from the XRD data and Scherrer’s formula. Transmission electron microscope (TEM) was used to analyze their structures. Room temperature magnetizations and coercivities of the samples in a magnetic field of 15 kOe have been determined from the hysteresis loops. It was found that magnetizations of the milled samples were smaller than the magnetization of the unmilled samples. This decrease, based on core-shell model, has been attributed to the presence of a magnetically dead layer on the particles’ surface of the milled powders. In addition, the magnetizations of the milled samples decrease with the increase in x value. This decrease has been discussed according to site occupation of the substituted cations on the sublattices. The discussion also supports the increase of lattice parameters and the decrease of Curie temperature as x increases.     

A new torsion-rotation fitting program for molecules with a sixfold barrier: Application to the microwave spectrum of toluene

A new program is described for fitting rotation-torsion energy levels in molecules like toluene, in which the frame (C₆H₅) has C_2v symmetry and the methyl top has C_3v symmetry, i.e., for molecules where the internal rotation barrier is expanded in cos6nα, where α is the internal rotation angle and n = 1,2,…. The program is based on the theoretical framework developed by Sørensen and Pedersen in their application of the Longuet-Higgins permutation-inversion group G₁₂ to the microwave spectrum of CH₃NO₂. It is specifically designed for sixfold barrier molecules, and allows the user to select almost any symmetry-allowed torsion-rotation term for inclusion in the fitting Hamiltonian. This program leads to a very successful fit of transitions in the microwave spectrum of toluene characterized by J ? 30, K_a ? 12, and by the free-rotor quantum number ∣m∣ ? 3. In these fits we included both published and rather extensive unpublished new measurements, for which fits using other torsion-rotation programs have not been very successful. The fit presented here uses 28 parameters to give an overall standard deviation of 7.4 kHz for 372 line frequencies, and results in a much improved value for the sixfold barrier for toluene, V₆ = 13.832068(3) cal mol⁻¹.     

“反胶团法”合成的CdS半导体纳米粒子的光谱性质研究

反相胶束是指由介于油和水界面的表面活性剂分子, 稳定、且均匀分散于连续油介质中的微液滴。它可以作为“微反应器”合成性能优良的CdS粒子。文章研究了反相胶束的W值(W=[水]/[表面活性剂])、[Cd2+]与[S2-]的比例和Cd2+和S2- 离子的起始浓度对CdS纳米粒子发光特性均有明显影响。回流处理可以对CdS纳米粒子的表面进行修饰,可以使CdS粒子的缺陷发光减弱并消失而显著增强激子发射,同时可增大粒径使激子发射峰位红移,体现了明显的量子限域效应; 所得材料的室温最大荧光量子效率高达11%。