Rapid reduction of titanium dioxide nano-particles by reduction with a calcium reductant

Micro-, submicron-, and nano-scale titanium dioxide particles were reduced by reduction with a metallic calcium reductant in calcium chloride molten salt at 1173 K, and the reduction mechanism of the oxides by the calcium reductant was explored. These oxide particles, metallic calcium as a reducing agent, and calcium chloride as a molten salt were placed in a titanium crucible and heated under an argon atmosphere. Titanium dioxide was reduced to metallic titanium through a calcium titanate and lower titanium oxide, and the materials were sintered together to form a micro-porous titanium structure in molten salt at high temperature. The reduction rate of titanium dioxide was observed to increase with decreasing particle size; accordingly, the residual oxygen content in the reduced titanium decreases. The obtained micro-porous titanium appeared dark gray in color because of its low surface reflection. Micro-porous metallic titanium with a low oxygen content (0.42 wt%) and a large surface area (1.794 m² g⁻¹) can be successfully obtained by reduction under optimal conditions.     

Enhanced photoluminescence properties of Sm ions in Cu and Sn co-doped P2O5:BaO glass

Luminescent glasses activated with Sm³⁺ ions are of current interest given their potential for a wide range of photonic applications. In this work, Sm³⁺-containing P₂O₅:BaO glasses are prepared by a simple melt-quench method, and the influence of CuO and SnO co-doping on Sm³⁺ photoluminescence (PL) is investigated. Optical absorption, solid-state ³¹P nuclear magnetic resonance spectroscopy, and PL spectroscopy are employed in the assessment of material optical and structural properties. The data indicates that monovalent copper ions and twofold-coordinated Sn centers are successfully stabilized in the matrix and both species can enhance the orange–red emission of Sm³⁺ ions. The optical properties of the material after heat treatment have been also assessed. Results indicate the chemical reduction of ionic copper via Sn²⁺ ultimately producing Cu nanoparticles as evidenced by the surface plasmon resonance. As a result, Sm³⁺ PL diminishes consistent with an excitation energy transfer to plasmonic Cu particles, i.e. the “plasmonic diluent” effect prevails.     

Luminescence and scintillation of Eu2+‐doped high silica glass

High silica glass doped with Eu²⁺ ions was prepared as a scintillating material by impregnation of Eu ions into a porous silica glass followed by reduction sintering in CO atmosphere. A dominant emission band of the Eu²⁺ 5d–4f transition peaking around 430 nm was observed in the luminescence spectrum with the excitation peak around 280 nm and no emission from Eu³⁺ was present. Photoluminescence decay kinetics was governed by decay times of a few microseconds. The Eu²⁺‐doped high silica glass exhibited comparable energy resolution and slightly higher photoelectron yield with respect to the Bi₄Ge₃O₁₂ crystal in the pulse height spectra for X‐ray photon energies within 22–60 keV. Furthermore, a factor of 1.2 higher radioluminescence intensity was observed as well. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Novel red perovskite phosphor Ca2AlNbO6:Eu for white light-emitting diode application

Eu³⁺-doped perovskite phosphors of Ca₂AlNbO₆ were synthesized from a solid state reaction. A small amount of the Li₂CO₃ flux was found to greatly shorten calcination time and reduce reaction temperature. The structural and optical properties of the samples were systematically investigated. The excitation spectra of Ca₂AlNbO₆:Eu³⁺ reveal two excitation bands at 398 (⁷F₀→⁵L₆) and 466 nm (⁷F₀→⁵D₂), which match well with the two popular emissions from near-UV and blue LED chips. Under blue light excitation, the red emission of Ca₂AlNbO₆:0.05Eu³⁺ is twice more intense than that of (Y_0.95Eu_0.05)₂O₃. The chromaticity coordinates of (Ca_0.95Eu_0.05)₂AlNbO₆ (x=0.654, y=0.346) are close to the standard values (x=0.670, y=0.330) of National Television Standard Committee (NTSC). The optical properties suggest that Ca₂AlNbO₆:Eu³⁺ is an efficient red-emitting phosphor for light-emitting diode applications.     

负折射率材料对产生Casimir排斥力的影响

研究了负折射率材料对产生Casimir排斥效应的影响. 两材料板间的Casimir排斥力的发生取决于两板以及其间媒质的电磁特性,通过理论与数值结果的分析研究给出电磁特性所影响排斥力的产生趋势. 对于由Drude-Lorentz型色散关系描述等效介电常数和磁导率的负折射率材料,调节各特征频率参数可实现Casimir排斥效应. 关键词： Casimir排斥力 负折射率材料 Drude-Lorentz型色散关系     

Effects of carbonization temperature on microstructure and electrochemical performances of phenolic resin-based carbon spheres

Activated phenol resin-based carbon spheres (APCS) electrodes with high double layer capacitance and good rate capability were prepared from phenol resin-based spheres (PS) at different carbonization temperatures prior to KOH activation. The carbonization temperature has a marked effect on both the pore structure and the electrochemical performances of the APCS in 6 M KOH electrolyte. APCS carbonized at 600 °C results in higher specific surface area and larger pore size, and hence higher capacitance and better rate capability. The specific capacitance of the APCS in 6 M KOH aqueous solution can be as high as 282 F g⁻¹. It remains 252 F g⁻¹ as the current density increases to 1000 mA g⁻¹.     

Fabrication and characterization of magnetic Fe3O4-CNT composites

Carbon nanotubes (CNTs) decorated with magnetite nanoparticles on their external surface have been fabricated by in situ solvothermal method, which was conducted in benzene at 500 °C with ferrocene and CNTs as starting reagents. The as-prepared composites were characterized using XRD, FTIR, SEM and TEM. It has been found that the amount of magnetite nanoparticles deposited on the CNTs can be controlled by adjusting the initial mass ratio of ferrocene to CNTs. The Fe₃O₄-CNT composites display good ferromagnetic property at room temperature, with a saturation magnetization value (M_s) of 32.5 emu g⁻¹ and a coercivity (H_c) of 110 Oe.     

Influence of gold nanoparticles on optically stimulated effects in TeO2-ZnO and GeO2-PbO amorphous thin films

We have found photoinduced second harmonic generation at wavelength 1064 nm during bicolor Nd:YAG laser coherent treatment of TeO₂-ZnO and GeO₂-PbO amorphous films. The maximally achieved second order susceptibility was equal to about 1.02 pm/V. Correlation of the induced second order susceptibility with local sample heating and induced birefringence may indicate an occurrence of local phase transitions from amorphous glass-like phase to non-centrosymmetry metastable phases.     

Reduction of surface coverage of finite systems due to geometrical steps

The coverage of vicinal, stepped surfaces with molecules is simulated with the help of a two-dimensional Ising model including local distortions and an Ehrlich-Schwoebel barrier term at the steps. An effective two-spin model is capable to describe the main properties of this distorted Ising model. It is employed to analyze the behavior of the system close to the critical points. Within a well-defined regime of bonding strengths and Ehrlich-Schwoebel barriers we find a reduction of coverage (magnetization) at low temperatures due to the presence of the surface step. This results in a second, low-temperature transition besides the standard Ising order-disorder transition. The additional transition is characterized by a divergence of the susceptibility as a finite-size effect. Due to the surface step the mean-field specific heat diverges with a power law.     

Strong water repellency effect on SiO<Subscript>2</Subscript> films processed at a nanometric scale

The present study deals with the creation of nano-rough surfaces with stable and controlled high hydrophobicity. These surfaces were obtained by combining the ion track etching technique with a simple functionalization by grafting perfluoroctyltrichlorosilane (PFOTS) molecules. Surface morphology was investigated by AFM observations which evidenced a self-affine fractal structure with a fractal dimension D_f ~ 2.6. The study of the wetting properties of these surfaces allowed to elucidate the conditions for observing a high hydrophobicity phenomenon and to predict the contact angle values for surfaces designed at a nanometric scale.