Synthesis and Crystal Structure of the Novel Compound Mg4.5Pr79.5Mo126O312 Containing Mo3, Mo7 and Mo19 Clusters

The synthesis and crystal structure of the novel reduced molybdenum oxide Mg_4.5Pr_79.5Mo₁₂₆O₃₁₂ are presented. This compound crystallizes in the trigonal space group R-3 m with a = 11.3061(2) Å, c = 58.242(1) Å, V = 6447.5(2) Å³, and Z = 1. Refinements yield R(F ²) = 0.0433 and wR(F ²) = 0.0931 for 2827 unique reflections. The structure is built up from alternating slabs made up of molybdenum forming Mo₃, Mo₇ and Mo₁₉ clusters, praseodymium and oxygen atoms, and slabs containing isolated MoO₆ octahedra. The Pr³⁺ cations are localized either within the slabs or at their borderlines to ensure the cohesion between the slabs. Of the six crystallographically independent sites occupy by the Pr³⁺ cations, two of them also contain randomly about 15% and 20% of Mg²⁺ cations while the remaining four are fully occupied by the Pr³⁺ cations.     

Ytterbium-catalyzed dual intermolecular hydrophosphination: synthesis of bis(phosphinyl)dienes and bis(alkenyl)phosphine oxides

Dual intermolecular hydrophosphination of conjugated diynes with 2 equiv of diphenylphosphine was catalyzed by ytterbium complexes, Yb(η²-Ph₂CNPh)(hmpa)₃ (1) and Yb[N(SiMe₃)₂]₃(hmpa)₂ (2), to give the corresponding 1,4-bis(diphenylphosphinyl)buta-1,3-dienes in high yields after oxidative work-up. Distribution of the four possible stereoisomers sharply depended on substituents of the substrates. (Z,Z)-Isomers were predominantly obtained from the disubstituted diynes, together with minor (Z,E)-isomers. On the other hand, the reaction of the terminal diynes provided major (E,Z) and minor (E,E)-butadienes. 1,4-Di-tert-butylbuta-1,3-diyne was exclusively converted to an allenic compound. Moreover, the dual hydrophosphination using phenyphosphine was also performed with 1 and 2. Thus, the reaction of 2 equiv of aromatic alkynes with PhPH₂ and subsequent oxidation gave bis(alkenyl)phosphine oxides in preference of the (Z,Z)-stereoisomers.     

Thermoelectric properties of homologous p- and n-type boron-rich borides

Thermoelectric properties of a series of layered homologous rare-earth boron carbonitrides: HoB₁₇CN, REB₂₂C₂N (RE=Y,Er,Lu), and YB_28.5C₄, were investigated. Samples for measurements were prepared in the form of hot pressed or isostatically pressed and annealed single phase polycrystalline powder. This series of compounds has structures where B₆ octahedral and rare-earth atomic layers reside between an increasing number of B₁₂ icosahedral and C-B-C chain layers, and has structural analogy to boron carbide. Interestingly, a variation from p-type thermoelectric behavior for YB_28.5C₄ to n-type for REB₂₂C₂N and HoB₁₇CN was observed. This is the first non-doped compound among the boron-rich borides in which n-type thermoelectric behavior has been observed. Similar to other boron cluster compounds low values of the thermal conductivity κ were found. The origins of the low κ in such compounds has not been fully explained, but comparison among the homologous series shows that the thermal conductivity appears to increase as the number of boron cluster layers increases. This result indicates that the heavy rare-earth atoms residing in the boron matrix may play a role in depressing thermal conductivity in addition to other features common to boron cluster compounds. Although the absolute values of the determined figures of merit ZT are not large for hot pressed samples, the Seebeck coefficients and power factors for both n-type and p-type in this series show an increase at temperatures exceeding 1000 K.     

稀土上转换发光材料标记抗体的制备及在免疫组化中的应用

采用微波辐射法合成了具有上转换发光特性的六方相纳米粒子NaGdF₄: Yb³⁺,Er³⁺(UCNPs), 其晶粒大小约为65 nm, 且粒子在980 nm的激发光下显示绿光(550 nm). 进一步在NaGdF₄: Yb³⁺,Er³⁺纳米晶的表面包覆了一层二氧化硅层, 进行氨基功能化后获得了表面共价结合氨基基团的粒径为70 nm的上转换发光纳米微球NaGdF₄: Yb³⁺,Er³⁺@SiO₂-NH₂(UCNPs@SiO₂-NH₂). 通过共价键将UCNPs@SiO₂-NH₂与多克隆抗体免疫球蛋白联接, 将标记后的多克隆抗体应用于传统的免疫组化检测子宫内膜腺细胞中基质金属蛋白酶组织抑制剂-4(TIMP-4)蛋白的表达. 结果表明, 微波合成的稀土上转换发光纳米材料形貌规则且粒径均一, 包覆硅壳后材料具有良好的分散性和水溶性, 荧光强度高且稳定, 在980 nm激发光下对生物组织无背景荧光, 可以很好地检测组织中蛋白质的表达.     

硼烯和碱土金属硼化物二维纳米材料的制备、结构、物性及应用研究

随着石墨烯研究的兴起,二维纳米材料得以迅速发展.在众多的二维纳米材料中,硼烯和碱土金属硼化物二维材料由于具有高费米速度、高杨氏模量、高透光性、高延展性、高度的各向异性、大的泊松比和高的化学稳定性等独特的性质,成为研究人员关注的焦点.本文侧重介绍目前硼烯和碱土金属硼化物二维纳米材料的制备工艺、结构、物性和应用情况.首先总结了目前硼烯的主要结构构型和制备及掺杂工艺;其次介绍了碱土金属硼化物二维纳米材料的理论结构构型和可能的制备路线;最后对硼烯和二维碱土金属硼化物纳米材料的物理特性进行归纳总结,同时预测它们未来最可能实现应用的领域.     

Cooperative luminescence quenching on many-particle acceptors in disordered media

Many-body cooperative energy transfer is an important process in biology, medicine, photosynthesis, rare-earth-doped laser materials, responsible for up- and down-conversion of energy, optical excitation sensitization and relaxation. We present an analytical solution for long-time asymptotic of static luminescence quenching kinetics due to cooperative energy transfer to ensembles of acceptors comprised of two-, three-, and more particles. For cooperative energy transfer and cooperative luminescence quenching to n-body acceptors we have discovered a new law of power d/(nS−(n−1)d)$d/(nS-(n-1)d)$ time dependence (d=1,2,3$d=1,2,3$ is the space dimension, S=6,8,10$S=6,8,10$ is the multipolarty of interaction: dipole–dipole, dipole–quadrupole, or quadrupole–quadrupole). The detailed numerical simulation of cooperative quenching by Monte-Carlo method confirms the theoretical result.     

Electronic structure and optical properties of TbNi5−xCux

In this paper we present theoretical investigation of optical conductivity for intermetallic TbNi_5−xCu_x series. Within the framework of LSDA+U calculations, electronic structure for x=0, 1, 2 is calculated and additionally optical conductivity is obtained. Disorder effects of Cu for Ni substitution on a level of LSDA+U densities of states (DOS) are taken into account via averaging over all possible Cu ion positions in the unit cell for given doping level x. Gradual smoothing of optical conductivity structure at 2 eV together with simultaneous intensity growth at 4 eV corresponds to increase of Cu and decrease of Ni content.     

Ce激活氯化钠在真空紫外光激发下的发光性质

采用水热蒸发法制备了NaCl∶Ce3+荧光粉,并通过X射线衍射(XRD)研究了材料的晶体结构。测量并分析材料在室温下的真空紫外激发光谱及相应的发射光谱。结果表明309和324nm的发射峰,对应于Ce3+离子的5d→4f(2 F5/2,2 F7/2)跃迁;激发谱显示6个峰,峰位分别为148,190,205,216,232和247nm。148nm的激发峰是基质吸收引起的;190,205,216,232和247nm是Ce3+的4f→5d跃迁引起的。