Yb：YAG晶体的合作发光现象

研究了Yb：YAG晶体的合作发光现象。当用940hm的近红外光激发时，Yb：YAG晶体有明显的上转换蓝色发光。实验发现498nm的蓝色发光强度与激发功率的平方成正比，而且Yb^3＋掺杂浓度越高，蓝色发光越强。分析表明这是Yb^3＋间强的相互作用导致的合作发光，是由于Yb^3＋在共价性的YAG基质中，它的4f^I3电子易于与近邻离子发生相互作用导致的。

Preparation and spectroscopic properties of Er3+-doped high silica glass fabricated by sintering nanoporous glass

A compact nonporous high silica (SiO2 % > 96%) glass containing 3400 ppm Er3+ ions, which was about ten times higher than that in Er-doped silica fiber amplifier (EDSFA), was synthesized by sintering porous glass immersed into erbium nitrate solution. The 1532 nm fluorescence has a FWHM (Full Width at Half Maximum) of 45 nm wider than that of EDSFA and possesses the glass with potential application in broadband fiber amplifiers. The Judd-Ofelt theoretical analysis reflects that Er3+ ions are located in a higher covalent environment which are comparable to those of aluminosilicate glass. (c) 2005 Elsevier B.V. All rights reserved.

Thermal, spectroscopic and laser properties of Yb3+Na+: CaF2 single crystals

The effects of Na+ doping level on the thermal conductivities, absorption and emission spectra, and fluorescence lifetimes of Yb3+ ,Na+ :CaF2 crystals were systematically studied. Sites structure, covalent force, and crystal field strength of Yb3+ :CaF2 crystals were markedly varied by codoping Na+ as charge compensator. The 2.0at% Yb3+ and 3.0at% Na+-codoped CaF2 crystal was demonstrated to operate in diode-pumped passively mode-locking scheme. Transform-limited 1 ps laser pulses were obtained, showing the crystal capable of producing ultra-short laser pulses. (c) 2006 Elsevier B.V. All rights reserved.

Purification and cloning of a novel C-type lectin-like protein with platelet aggregation activity from Trimeresurus mucrosquamatus venom

TMVA, a novel C-type lectin-like protein that induces platelet aggregation in a dose-dependent manner, was purified from the venom of Trimeresurus mucrosquamatus. It consists of two subunits, alpha (15,536 Da) and beta (14,873 Da). The mature amino acid sequences of the a (135 amino acids) and beta subunits (123 amino acids) were deduced from cloned cDNAs. Both of the sequences show great similarity to C-type lectin-like venom proteins, including a carbohydrate recognition domain. The cysteine residues of TMVA are conserved at positions corresponding to those of flavocetin-A and convulxin, including the additional Cys135 in the alpha subunit and Cys3 in the beta subunit. SDS-PAGE, mass spectrometry analysis and amino acid sequence showed that native TMVA exists as two convertible multimers Of (alphabeta)(2) and (alphabeta)(4) with molecular weights of 63,680 and 128,518 Da, respectively. The (alphabeta)(2) complex is stabilized by an interchain disulfide bridge between the two alphabeta-heterodimers, whereas the stabilization of the (alphabeta)(4) complex seems to involve non-covalent interactions between the (alphabeta)(2) complexes. (C) 2002 Elsevier Science Ltd. All rights reserved.

First-principles study of UC2 and U2C3

The electronic structure and mechanical properties Of UC2 and U2C3 have been systematically investigated using first-principles calculations by the projector-augmented-wave (PAW) method. Furthermore, in order to describe precisely the strong on-site Coulomb repulsion among the localized U 5f electrons, we adopt the generalized gradient approximation +U formalisms for the exchange-correlation term. We show that our calculated structural parameters and electronic properties for UC2 and U2C3 are in good agreement with the experimental data by choosing an appropriate Hubbard U = 3 eV. As for the chemical bonding nature, the contour plot of charge density and total density of states suggest that UC2 and U2C3 are metallic mainly contributed by the 5f electrons, mixed with significant covalent component resulted from the strong C-C bonds. The present results also illustrate that the metal-carbon (U-C) bonding and the carbon-carbon covalent bonding in U2C3 are somewhat weaker than those in UC2, leading to the weaker thermodynamic stability at high temperature as observed by experiments.

Mechanical and chemical bonding properties of ground state BeH2

The crystal structure, mechanical properties and electronic structure of ground state BeH2 are calculated employing the first-principles methods based on the density functional theory. Our calculated structural parameters at equilibrium volume are well consistent with experimental results. Elastic constants, which well obey the mechanical stability criteria, are firstly theoretically acquired. The bulk modulus B, Shear modulus G, Young's modulus E, and Poisson's ratio upsilon are deduced from the elastic constants. The bonding nature in BeH2 is fully interpreted by combining characteristics in band structure, density of states, and charge distribution. The ionicity in the Be-H bond is mainly featured by charge transfer from Be 2s to H 1s atomic orbitals while its covalency is dominated by the hybridization of H 1s and Be 2p states. The Bader analysis of BeH2 and MgH2 are performed to describe the ionic/covalent character quantitatively and we find that about 1.61 (1.6) electrons transfer from each Be (Mg) atom to H atoms.

First-principles study of ground-state properties and high pressure behavior of ThO2

The mechanical properties, electronic structure and phonon dispersion of ground state ThO2 as well as the structure behavior up to 240 GPa are studied using first-principles density-functional theory. Our calculated elastic constants indicate that both the ground-state fluorite structure and high pressure cotunnite structure of ThO2 are mechanically stable. The bulk modulus, shear modulus, and Young's modulus of cotunnite ThO2 are all smaller by approximately 25% compared with those of fluorite ThO2. The Poisson's ratios of both structures are approximately equal to 0.3 and the hardness of fluorite ThO2 is 22.4 GPa. The electronic structure and bonding nature of fluorite ThO2 are fully analyzed, and show that the Th-O bond displays a mixed ionic/covalent character. The phase transition from the fluorite to cotunnite structure is calculated to occur at the pressure of 26.5 GPa, consistent with recent experimental measurement by ldiri et al. [1]. For the cotunnite phase it is further predicted that an isostructural transition takes place in the pressure region of 80-130 GPa.

Structural, mechanical, thermodynamic, and electronic properties of thorium hydrides from first-principles

We perform first-principles calculations of the structural, electronic, mechanical, and thermodynamic properties of thorium hydrides (ThH2 and Th4H15) based on the density functional theory with generalized gradient approximation. The equilibrium geometries, the total and partial densities of states, charge density, elastic constants, elastic moduli, Poisson's ratio, and phonon dispersion curves for these materials are systematically investigated and analyzed in comparison with experiments and previous calculations. These results show that our calculated equilibrium structural parameters are well consistent with experiments. The Th-H bonds in all thorium hydrides exhibit weak covalent character, but the ionic properties for ThH2 and Th4H15 are different due to their different hydrogen concentration. It is found that while in ThH2 about 1.5 electrons transfer from each Th atom to H, in Th4H15 the charge transfer from each Th atom is around 2.1 electrons. Our calculated phonon spectrum for the stable body-centered tetragonal phase of ThH2 accords well with experiments. In addition we show that ThH2 in the fluorite phase is mechanically and dynamically unstable.

Structural, elastic, and electronic properties of cubic perovskite BaHfO3 obtained from first principles

We investigated the structural, elastic, and electronic properties of the cubic perovskite-type BaHfO3 using a first-principles method based on the plane-wave basis set. Analysis of the band structure shows that perovskite-type BaHfO3 is a wide gap indirect semiconductor. The band-gap is predicted to be 3.94 eV within the screened exchange local density approximation (sX-LDA). The calculated equilibrium lattice constant of this compound is in good agreement with the available experimental and theoretical data reported in the literatures. The independent elastic constants (C-11, C-12, and C-44), bulk modules B and its pressure derivatives B', compressibility beta, shear modulus G, Young's modulus Y, Poisson's ratio nu, and Lame constants (mu, lambda) are obtained and analyzed in comparison with the available theoretical and experimental data for both the singlecrystalline and polycrystalline BaHfO3. The bonding-charge density calculation make it clear that the covalent bonds exist between the Hf and 0 atoms and the ionic bonds exist between the Ba atoms and HfO3 ionic groups in BaHfO3. (C) 2009 Elsevier B.V. All rights reserved.

Growth of heavily Zn-doped InGaAs at low temperature by LP-MOCVD

Epitaxial growth of Zn-doped InGaAs on InP substrates has been carried out at 550degreesC by LP-MOCVD. Hole concentration as high as 6 x 10(19)cm(-3) has been achieved at the H-2 flow rate of 20 sccm through DEZn bubbler. The lattice constant of Zn-doped InGaAs was found to be dependent on the flow rate of DEZn, and the tensile strain mismatch increases with increasing H-2 flow rate of DEZn. The negative lattice mismatch of heavily Zn-dopped InGaAs may be due to, the small covalent bonding radius of zinc and the combination of butane from ethyl of DEZn,and TEGa. And the latter accelerates the pyrolysis of TEGa, which is the dominant mechanism in determining the negative mismatch of Zn-doped InGaAs. (C) 2003 Elsevier B.V. All rights reserved.

Influence of dual incorporation of In and N on the luminescence of GaInNAs/GaAs single quantum wells

The optical properties of above- and below-band-edge transitions have been investigated by incorporating In atoms into GaNAs/GaAs single quantum wells. The experimental results show that with increasing In concentration the interband luminescence is improved and the luminescence intensity below the band edge in GaInNAs/GaAs decreases significantly. An interpretation is given that N atoms are preferable to form a covalent bond with In than with Ga atoms in a GaInNAs alloy, due to the compensation of the atomic-size difference between In and N atoms on the GaAs substrate. The photoreflectance spectra of the GaInNAs/GaAs single quantum well support the assignment of an intrinsic mechanism to the high-energy luminescence peak. (C) 2000 American Institute of Physics. [S0003- 6951(00)01752-6].

Electronic, structural, and optical properties of crystalline yttria

The electronic structure of crystalline Y2O3 is investigated by first-principles calculations within the local-density approximation (LDA) of the density-functional theory. Results are presented for the band structure, the total density of states (DOS), the atom-and orbital-resolved partial DOS. effective charges, bond order, and charge-density distributions. Partial covalent character in the Y-O bonding is shown, and the nonequivalency of the two Y sites is demonstrated. The calculated electronic structure is compared with a variety of available experimental data. The total energy of the crystal is calculated as a function of crystal volume. A bulk modulus B of 183 Gpa and a pressure coefficient B' of 4.01 are obtained, which are in good agreement with compression data. An LDA band gap of 4.54 eV at Gamma is obtained which increases with pressure at a rate of dE(g)/dP = 0.012 eV/Gpa at the equilibrium volume. Also investigated are the optical properties of Y2O3 up to a photon energy of 20 eV. The calculated complex dielectric function and electron-energy-loss function are in good agreement with experimental data. A static dielectric constant of epsilon(O)= 3.20 is obtained. It is also found that the bottom of the conduction band consists of a single band, and direct optical transition at Gamma between the top of the valence band and the bottom of the conduction band may be symmetry forbidden.

环糊精非共价复合物和黄芪皂甙的质谱研究

首先，由于电喷雾质谱技术已被广泛的应用于研究非共价复合物。为了深入揭示环糊精复合物和气液两相相关性，本章系统的研究了α，β两种环糊精和联苯胺的包合物，并分别用IHNMR和荧光光谱表征了其在液相中的行为，用ESI-MS，表征了他们在气相中的行为。ESI-MS检测这些复合物发现：两种环糊精都与benzidine形成较稳定的1:1复合物，-CD还能与benzidine形成2:1的复合物。这也部分证明了环糊精基于分子大小和空间结构匹配的分子识别作用。通过这些特异性复合物在气液两相中行为的相关性研究，证实了复合物离子的相对强度，相对碰撞诱导解离（CID）与其液相稳定性相一致。本文还研究了α-CD和二茂铁衍生物的非共价复合物的电喷雾质谱，实验结果表明非共价复合物的物质的量的比为1:1，通过循环伏安的电化学方法提出了两种可能存在的包合物的结构。我们对黄茂中的皂甙化合物进行了提取和分离，并成功的应用电喷雾多级串联质谱技术跟踪监测混合物中的皂贰化合物，建立混合物中便捷，实用，高效的测定皂贰的质谱方法。来用电喷雾多级串联质谱技术，研究了正负离子条件下传统中药黄茂中的有效成分黄蔑甲贰的特征质谱行为，确定了小柱梯度淋洗的条件，可以此鉴定传统黄芪中有效成分，为传统黄芪药材及相关药品的快速鉴别和质量控制具有重要意义。利用质谱技术为研究手段，深入探讨了碱金属离子对黄茂甲贰结构分析的影响，发现在相同的碰撞活化诱导解离能的条件下，锂离子的加合物能够给出更丰富的碎片离子信息。

毛蕊异黄酮类似物的合成及其对JAK/STAT信号途径调控的构效关系研究

干扰素（IFNs）是最早发现的具有广泛用途的一类细胞因子，IFN-α通过JAK/STAT信号途径调控机体一系列生理和病理反应。至今尚未发现类干扰素的小分子。我们前期研究发现天然产物毛蕊异黄酮可激活干扰素诱导的JAK/STAT信号途径。为发现类干扰素小分子、获得小分子探针，本课题拟建立成熟的JAK/STAT信号途径的筛选模型，合成毛蕊异黄酮及其类似物，研究这些化合物的构效关系，进而尝试通过共价键标记生物素或香豆素来直接研究它们与相关受体的作用。 从异香草醛出发经7步合成反应得到了毛蕊异黄酮。采用平行合成策略得到异黄酮类化合物；采用分支式合成策略，以取代苯乙酸作为合成砌块，获得具有与异黄酮类似结构的香豆素、3-芳基喹诺酮。与分离得到的黄酮类化合物，构建了一个包括异黄酮、黄酮、香豆素、3-芳基喹诺酮在内的化合物库。 建立了包含IFN-α刺激反应元件 (ISRE)的荧光素酶报告基因体系，通过筛选化合物库中的化合物，发现异黄酮骨架为激活JAK/STAT信号途径必须结构、毛蕊异黄酮7-位酚羟基被取代后活性丧失。根据以上结果，对毛蕊异黄酮3′-位标记物的合成进行了初步尝试。 发现山茱萸科植物青荚叶(Helwingia japonica (Thunb.) Dietr.)有抑制蛋白酪氨酸磷酸酯酶1B（PTP1B）的活性。从其地上部分95%乙醇提取物的乙酸乙酯部分分离得到5个化合物,应用波谱方法及与已知品对照的手段鉴定它们为p-menth-2-en-1β, 4β, 8-triol (Z-1)、blumenol A (Z-2)、2′,3′,4′,5′,6′-五羟基查尔酮(Z-3)、洋芹素7-O-β-D-吡喃葡萄糖苷(Z-4)、木犀草素7-O-β-D-吡喃葡萄糖苷(Z-5). Interferons (IFNs) are one kind of cytokines with broad functions. IFN-α mediates series physiological and pathological changes of human body via JAK/STAT pathway. Untill now, no IFNs-like small molecules are discovered. In our preliminary experiment, the natural product calycosin has been observed to activate JAK/STAT pathway. Therefore, we establish a luciferase reporter gene system and synthesize calycosin and its analogues to reveal their structure-activity relationship (SAR). Besides, in order to prove that calycosin activates JAK/STAT pathway through IFN receptor, we attempted to tag it with biotin or coumarin by covalent bonding. Calycosin was synthesized from isovanillin via seven steps. Other isoflavones were obtained by parallel synthesis; coumarins and quinolones were prepared through divergent synthesis, using substituted phenylacetic acids as building blocks. Combing with natural flavones, a small molecule library was established. A luciferase reporter gene system, consisting of 5 copies of the ISRE (interferon-stimulated response element), was used for screening of small molecules from that library. We found that the core-structure of isoflavone was necessary, and if the 7-OH is substituted, the activity slumps. According to our observation, we tried to tag biotin or coumarin at 3′-OH of calycosin. The 95% ethanol extract of the aerial parts of Helwingia japonica (Thunb.) Dietr. showed protein tyrosine phosphatase 1B (PTP1B) inhibitory activity. Five compounds were isolated. On the basis of spectral data or by comparison with authentic samples, they were identified as p-menth-2-en-1β,4β,8-triol (1), blumenol A (2), 2′,3′,4′,5′,6′-pentahydroxychalcone (3), apigenin 7-O-β-D-glucopyranoside (4), and luteolin 7-O-β-D-glucopyranoside (5).

Study on nanohardness of helium-implanted 4H-SiC

The hardness of 4H-SiC, which was high-temperature (500 K) helium-Implanted to fluences of 3 x 10(16) Ions cm(-2) and subsequently thermally annealed at the temperature ranging from 773 to 1273 K, was studied by nanoindentation It is found that the hardness of the implanted 4H-SiC increases at the first, then decreases, and then increases again with increasing annealing tempeature in the temperature range of 500-1273 K, and significant increase in hardness is observed at 773 K. The behavior is ascribed to the changes of the density, length, and tangling of the covalent Si-C bond through the recombination of point defects, clustering of He-vacancy, and growth of helium bubbles during the thermal annealing