Advanced Materials Research Vols. 690-693

Abstract: Zinc oxide doped with Eu³⁺ ions red emitting phosphors were prepared by precipitation method, and its luminescence properties were investigated. The phosphors were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and photoluminescence (PL) spectra. The ZnO:Eu³⁺ phosphors were obtained at 600°C by calcining precipitation precursor. These phosphors can be effectively excited at 465nm. In emission spectra, the strongest peak at 616nm correlating to red emission is due to the electric dipole transition ⁵D₀⁷F₂ of Eu³⁺ ions. Eu³⁺ions replaced Zn²⁺ ions and occupied the non-centrosymmetric sites in the ZnO matrix lattice. The phosphor particles with narrow distribution range are approximately 100-200nm in size. The luminescence properties of ZnO:Eu³⁺ phosphor with 8 mol% doping concentration of Eu³⁺ is optimal.

Abstract: By means of the full potential linearized augmented plane-wave method based on the first-principle study, we calculate the structure, electronic and magnetic properties of full-Heusler alloy Co₂CrGa. Our results show that full-Heusler alloy Co₂CrGa is ferromagnetic ground state with a magnetic moment of 3.03774 μ_B per formula unit. Importantly, the calculated spin polarization around the Fermi level is very high up to 93.2%, which indicates that full-Heusler alloy Co₂CrGa would be possibly applied to the field of the material engineering and spintronic devices.

Abstract: The wide band gap, temperature stability, high resistivity, robustness of semiconducting boron carbide make it an attractive material for device applications.. Here the structural stability along with the electronic and the optical properties of Ni-doped boron carbides (B₁₃C₂) were studied using the first principle calculations based on plane wave pseudo-potential theory. The calculated results showed that Ni-doped in boron carbide was in preference to substituting C atom on the end of C-B-C chain, but it was difficult for Ni to substitute B atom in the center of the C-B-C chain or in the icosahedron. A representative stable structural unit containing Ni atom was [C-B-N ^ε+-[B₁₁ ^ε-, while the structural unit without Ni was [C-B- ^ε--[B₁₂] ^ε+. The band structure, density of states (DOS) indicated that the coexistence of [C-B-N ^ε+-[B₁₁ ^ε- structural unit made electrical conductivity increased. Some new impurity energy levels appear in the band gap of Ni-doped B₁₃C₂, which can improve the conductivity of B₁₃C₂ as well. Ni acts as a n-type dopant. As the covalent bond of Ni-B was weaker than those of B-B and B-C, the thermal conductivity decreased for Ni-doped B₁₃C₂, thermoelectric property of Ni-doped boron carbides has been improved. The imaginary part of the dielectric function of Ni-doped B₁₃C₂ has three remarkable peaks at 1.13, 3.89, and 6.05 eV. This reveals that doping with Ni can improve the photo-absorption efficiency of B₁₃C₂.

Abstract: A type n conductance of ZnO thin film was deposited on the p-Si filim by magnetron sputtering Al doped ZnO ceramic target, and the ZnO/p-Si heterojunction was preparated. The photoelectric properties, charge carrier transport mechanism were studied by testing the I-V, C-V characteristics with illumination and without illumination. The results shows that there exists a good rectifying properties and photoelectric response for ZnO/p-Si heterojunctions, and can be widely used in photoelectric detection and fields of solar cells. As the conduction band and valence band offset in the ZnO/p-Si heterojunction is too big, the current transport mechanism is dominated by the space-charge limited current (SCLC) conduction at the forward voltage exceeds 1 V. The results suggest the existence of a large number of interface states in ZnO/p-Si heterojunction, and the interface states can be reduced and the photoelectric properties can be further improved.

Abstract: All electronic structures and infrared adsorption spectra of AgnH2S (n=3, 5) clusters have been performed by using density functional theory. We obtain the lowest-energy structures of Ag3, Ag5, Ag3H2S and Ag5H2S clusters. The calculation results show that the lowest-energy structures of Ag3 and Ag5 clusters are planar geometries. The lowest-energy structures of Ag3H2S and Ag5H2S can be obtained by adsorbs immediately H2S on Ag3 and Ag5 clusters. The peak of infrared spectrum is 120cm-1 for Ag3 cluster, which is smaller than that of Ag5 cluster (180 cm-1). The peak of infrared spectrum is 350cm-1 for Ag3H2S cluster, which is larger than that of Ag5H2S cluster (290 cm-1). The comparison illustrates that adsorption H2S molecule make the peak of infrared spectrum shifting to shortwave.

Abstract: Three stilbene-eighteen alkyl quaternary ammonium salts were synthesized through three-step reactions. The physical properties of compounds were characterized by UV and fluorescence emission spectra. The new compounds were applied to cotton fiber as fluorescent brightening agents and their performances were evaluated by measuring the degree of whiteness. The surface tension (γ) and the Critical Micelle Concentration (CMC) of compounds were evaluated. The results showed that the three compounds could greatly reduce the surface tension of aqueous solutions.

Abstract: Novel hole-transporting materials (M1, M2) containing triphenylamine and dipyridine units have been synthesized and characterized. Two compounds have excellent solubility in common solvents. The optical, electrochemical and thermal properties of the materials were studied in detail. The results show that two compounds have green emission in dichloromethane, high thermal stability and proper HOMO levels. The properties of compounds M1 and M2 indicate that two compounds are candidates for the application in Organic light-emitting devices as hole-transporting materials.

Abstract: We perform first-principles calculations to investigate the band structure and density of states of rare-elements doped ZnO. The calculated results show that the shapes of band structures for ZnO by rare-element doping are similar. And the rare-elements incorporation has a little influence on the band gap of the doping system under our considered doping concentration, but after doping, the Fermi level goes into the conduction band, and the electrons from the conduction band minimum to the Fermi level are increasing after rare-earth doping, which means that rare-element doping can change the electrical conductivity of ZnO to a great extent. Meanwhile, it is found that the conduction band near the Fermi level is determined by the rare-element-d states and O-p states, demonstrating as a strong hybridization. This study could provide a theoretical explanation for the factors influencing the properties of ZnO.

Abstract: ZnGa₂O₄ phosphors have been synthesized by solid state reaction at different temperatures with different B₂O₃ concentration incorporated in the experiments. All samples present green (509 nm) and red (696 nm) emission bands under ultraviolet excitation (250 nm), whose intensity changes because of the increasing B₂O₃ contents. The green and the red long afterglow have been observed after removing the ultraviolet light and the performance largely improves with the introduction of B₂O₃. The effects of the doping contents of B₂O₃ as well as the sintering temperatures on the luminescent properties of the obtained products have been investigated. The introduction of B₂O₃ changes the ratio of the two emitting centers and increases the depth of the trap centers in the samples.

Abstract: This paper has developed one way to produce flexible carbon cloth from artificial cotton cloth carbonized at 1000°C with using (NH₄)₂HPO₄ as impregnation agent and phenolic resin as modification agent. The effects of (NH₄)₂HPO₄ and phenolic resin on bulk resistivity, tensile strength, density, thickness and microstructure of the resultant carbon cloth were investigated. The results show that (NH₄)₂HPO₄ impregnation is helpful to increase the carbon yield of artificial cotton cloth and decrease the bulk resistivity. The fibers in the carbon cloth are bond by carbonized phenolic resin, leading to higher tensile strength and lower bulk resistivity. When mass content of (NH₄)₂HPO₄ was 5% and phenolic resin 54%, flexible and porous carbon cloth was prepared with thickness of 0.27mm, density of 0.34g/cm³, bulk resistivity of 0.06Ω·cm and tensile strength of 2.33MPa, which is promising materials for diffusion layer in fuel cell.