Synthesis and photophysical properties of Ir<Superscript>III</Superscript>-Ln<Superscript>III</Superscript> (Ln = Nd,Yb, Er) bimetallic complexes containing bipyrimidines as bridging ligands

Bipyrimidines have been chosen as (N∧N)(N∧N) bridging ligands for connecting metal centers. Ir^III-Ln^III (Ln = Nd, Yb, Er) bimetallic complexes [Ir(dfppy)₂(μ-bpm)Ln(TTA)₃]Cl were synthesized by using Ir(dfppy)₂(bpm)Cl as the ligand coordinating to lanthanide complexes Ln(TTA)₃·2H₂O. The stability constants between Ir(dfppy)₂(bpm)Cl and lanthanide ions were measured by fluorescence titration. The obvious quenching of visible emission from Ir^III complex in the Ir^III-Ln^III (Ln = Nd, Yb, Er) bimetallic complexes indicates that energy transfer occurred from Ir^III center to lanthanides. NIR emissions from Nd^III, Yb^III, and Er^III were obtained under the excitation of visible light by selective excitation of the Ir^III-based chromophore. It was proven that Ir(dfppy)₂(bpm)Cl as the ligand could effectively sensitize NIR emission from Nd^III, Yb^III, and Er^III.     

壳聚糖-聚丙烯酰胺接枝共聚物接枝率的测定

根据溶液的折光指数增量与溶液的组成间存在定量关系的原理提出了一种测定接枝聚合物接枝率的新方法, 并用此方法测定了壳聚糖-聚丙烯酰胺接枝共聚物的接枝率. 结果通过元素分析法测定样品中氮元素的百分含量, 以及运用折光指数增量法测定已知比例的壳聚糖与聚丙烯酰胺(PAM)混合物中二者的质量百分比进行佐证. 结果表明, 折光指数增量法测定接枝共聚物的接枝率也是可行的.     

Asymmetric Michael addition of aldehydes to nitroolefins catalyzed by l-prolinamide derivatives using phenols as co-catalysts

The asymmetric Michael addition of aldehydes to nitroolefins was investigated using l-prolinamide derivatives of 2-(2′-piperidinyl)pyridine as catalyst and a variety of phenols as co-catalyst. Extensive screening toward the effect of prolinamides, phenols, and solvents on this transformation revealed that a combination of (S)-2-(2′-piperidinyl)pyridine-derived trans-4-hydroxy-l-prolinamide 2c, (S)-1,1′-bi-2-naphthol, and dichloromethane was a promising system. This system was shown to be amenable to a rich variety of aldehydes and nitroolefins and afforded the nitroaldehyde products with excellent yield, enantiomeric excess (up to 99%) and diastereoselectivity ratio (up to 99/1), even in the case of 1 mol % catalyst loading and 1.5 equiv of aldehydes.     

Li/LiFePO4 batteries with room temperature ionic liquid as electrolyte

Room temperature ionic liquid (RTIL) was prepared on basis of N-methyl-N-butylpiperidinium bis(trifluoromethanesulfonyl)imide (PP₁₄TFSI), which showed a wide electrochemical window (?0.1–5.2 V vs. Li⁺/Li) and is theoretically feasible as an electrolyte for batteries with metallic Li as anodes. The addition of vinylene carbonate (VC) improved the compatibility of PP₁₄TFSI-based electrolyte towards lithium anodes and enhanced the formation of solid electrolyte interphase film to protect lithium anodes from corrosion. Accordingly, Li/LiFePO₄ cells initially delivered a discharge capacity of about 127 mAh g^?1 at a current density of 17 mA g^?1 in the ionic liquid with the addition of VC and showed better cyclability than in the neat ionic liquid. Electrochemical impedance spectroscopy disclosed that the addition of VC enhanced Li-ion diffusion and depressed interfacial resistance significantly.     

Solvothermal growth and morphology study of Cu2Se films

Solvothermal growth of cuprous selenide films on copper substrate has been succeeded by treating copper foil in the mixture of selenium powder and amines or hydrazine. The films were characterized by methods of XRD, SEM, TEM and optical spectra (Cu₂Se, JCPDS 47-1448). Films with hexagonal microcrystals can be obtained in hydrazine/water reaction system. When CTAB (CTAB = cetyltrimethylammonium bromide) is added to the system, the film is composed of thin leaf-like microcrystals. When ethylenediamine (en) is used as solvent, the leaf-like microcrystals are crimped.     

Study on the Failure Factors of Composite Insulation in High-Voltage Storage Capacitors

High-voltage storage capacitors, which have composite insulations of polypropylene film and paper impregnated with oil, are working under charge–discharge mode. The insulations are not only exposed to electrical stress but also to thermal stress. Failure factors of composite insulation in capacitors are analyzed from three aspects: partial discharge (PD), space charge, and thermal factors. In order to investigate the possible influences on the dielectric properties of materials in capacitors, aging tests were conducted on the capacitors. Some parameters were detected in aged capacitors compared with nonaged ones. Experimental results reveal that PD is the key factor leading to the breakdown of the capacitor, space charge is the direct factor that induces the breakdown, and thermal factor just accelerates the degradation process.      

A red oxide phosphor, Sr2ScAlO5:Eu2+ with perovskite-type structure, for white light-emitting diodes

Sr2ScAlO5:Eu2+,a red oxide phosphor with a perovskite-type structure,has been synthesized through a solid-state reaction and its luminescence properties have been investigated.An absorption band centering at 450 nm is observed from the diffuse reflection spectra and the excitation spectra,indicating that the phosphor can match perfectly with the blue light of InGaN light-emitting diodes.A broad red emission band at 620 nm is found from the emission spectra,originating from the 4f 6 5d-4f 7 transition of the Eu 2+ ions.The best doping content of Eu in this material is about 5%.Sr2ScAlO5:Eu2+is a highly promising red phosphor for use in white light-emitting diodes.     

Efficient diode-pumped passively Q-switched laser with Nd:YAG/Cr:YAG composite crystal

Diffusion bonded Nd:YAG/Cr:YAG composite laser crystal has been employed to perform a compact diode-pumped passively Q-switched laser. At the incident pump power of 3.3 W and pulse repetition rate of 16.3 kHz, the maximum average output of 592 mW has been obtained, corresponding to an optical-to-optical conversion efficiency of 18%. Stable passively Q-switched operation with peak power of 6.5 kW and pulse duration of 6 ns was also achieved. It has been experimentally revealed that Nd:host/Cr:YAG composite structure is a promising material for compact cost-effective Q-switched laser sources with high-peak power and short pulse duration. In addition, thermal lens effect (TLE) in the active medium and its impact on the Q-switched laser performance have been analyzed.     

Vibrational and thermodynamic properties of metals from a model embedded-atom potential

This work provides the first systematic test of validity of the embedded-atom potentials of Mei et al. [Phys. Rev. B 43 (1991) 4653], via a complete study of the vibrational and thermodynamic properties of isoelectronic transition (Ni, Pd, Pt) and noble (Cu, Ag, Au) metals. Phonon dispersion curves and thermal properties are studied within the quasiharmonic approximation. Results for the temperature-dependence of the lattice constants, coefficients of linear thermal expansion, isothermal and adiabatic bulk moduli, heat capacities at constant volume and constant pressure, Debye temperatures and Grüneisen parameters are presented. Electronic contribution to the specific heat is included explicitly via density-functional calculation. The calculated phonon frequencies for Ag and Cu agree well with the results from inelastic neutron scattering experiments. Despite less satisfactory agreement between calculated and measured phonon frequencies for the other four metals, isothermal and adiabatic bulk moduli and the specific heats of all metals are reproduced reasonably well by the model, while the Grüneisen parameter and Debye temperature are underestimated by about 10%. The coefficient of linear thermal expansion is underestimated with respect to measured values in most cases except for Pt and Au. The results are good for Pt up to 1000 K and for Au up to 500 K.     

Shape transition and propulsive force of an elastic rod rotating in a viscous fluid

The deformation of an elastic rod rotating in a viscous fluid is considered, with applications related to flagellar motility. The rod is tilted relative to the rotation axis, and experiments and theory are used to study the shape transition when driven either at constant torque or at constant speed. At low applied torque, the rod bends gently and generates small propulsive force. At a critical torque, the rotation speed increases abruptly, and the rod forms a helical shape with increased propulsive force. We find good agreement between theory and experiment. A simple physical model is presented to capture and explain the essential behavior.