Beifang Yang

Synthesis of Ag/ZnO nanorods array with enhanced photocatalytic performance

Silver-modified ZnO nanorods array has been prepared and the effect of silver modification has been studied. ZnO nanorods array were fabricated through a wet chemical route and a photo deposition method was taken to fabricate silver nano particulate on the ZnO nanorods. The structural and optical properties were characterized by field emission scanning electron microscope, high resolution transmission electron microscope, X-ray photoelectron spectroscopy, Raman, UV-vis and photoluminescence (PL) spectra. The UV photocatalytic activity of these materials was studied by analyzing the degradation of methylene blue (MB) in aqueous solution. The photocatalytic performance indicated that Ag deposit acted as not only electron sinks to enhance the separation of photoexcited electrons from holes, but also charge carrier recombination centers, so the optimized amount of Ag deposit was investigated.

An intense ultraviolet photoluminescence in sol?gel ZnO?SiO2 nanocomposites

We report the phenomenon that the intensity of the ultraviolet (UV) photoluminescence (PL) from ZnO was greatly enhanced by incorporating ZnO into the SiO2 matrix. PL excitation results show that both the ZnO nanoparticles and the SiO2 matrix in the nanocomposites contribute to the luminescence process for the UV band. On the basis of the x-ray photoelectron spectra, we suggest that interface energy states are formed due to the presence of Zn?O?Si bonds between ZnO nanoparticles and the SiO2 matrix. A tentative model concerning the contribution of the ZnO nanoparticles, SiO2 matrix, and ZnO?SiO2 interface is suggested to explain the PL enhancement effect.

Amplified spontaneous emission of an Nd3+-doped poly(methyl methacrylate) optical fiber at ambient temperature

Polymer optical fibers have received much attention in recent years as they can replace silica glass fibers in local area nets in the future. A neodymium ion (Nd3+)-doped poly(methyl methacrylate) (PMMA) fiber has been made from Nd3+ containing PMMA as a core and silica resin as claddings. Fluorescence of the fiber results from the transition of 4G5/2 to 4I9/2 in a three energy level system. Amplified spontaneous emission (ASE) at 575 nm has also been observed and the critical power at a pump wavelength of 514.5 nm for the onset of ASE has been found to be 85 mW.

Correlation between 577cm−1 Raman scattering and green emission in ZnO ordered nanostructures

We have investigated resonant Raman scattering (RRS) and photoluminescence of ZnO inverse opal prepared by electrodeposition. The intensities of both 577cm−1 Raman scattering and green emission get weaker after aging or UV laser irradiation. The RRS and green emission intensities are highly correlated for different samples, regardless of the means of sample treatment. According to the deposition-temperature and annealing-temperature dependences, we propose that the origins of the two peaks are related to surface hydroxide.

Enhanced yellow–green photoluminescence from ZnO–SiO2 composite opal

A remarkably enhanced yellow–green photoluminescence (PL) was observed from ZnO nanocrystals infiltrated into SiO2 opal photonic crystals. It was clearly visible to the naked eye under the excitation of an Xe lamp and had substantially improved thermal stability over pure ZnO nanocrystals. The PL spectrum shape of a ZnO–SiO2 composite opal can be modified by annealing an SiO2 opal or choosing an SiO2 opal with different lattice parameters. The enhancement of PL intensity is interpreted based on the dependence of the PL intensity on the size of SiO2 microspheres as well as the anisotropy of the photoluminescence excitation (PLE) spectra. Our results may be interesting for further application.

Thin SiC films prepared by pyrolysis of polyimide Langmuir–Blodgett films on silicon

The quasi‐single‐crystal SiC thin films were grown on silicon (111) by pyrolysis of polyimide LB films at 1000 °C in vacuum. The chemical and structural characterizations were studied by x‐ray diffraction, infrared absorption, x‐ray photoelectron spectroscopy, and Laue photography.

Intense ultraviolet photoluminescence from amorphous Si:O:C films prepared by liquid–solution-phase technique

Abstract Intense ultraviolet (UV) photoluminescence (PL) was observed at room temperature from amorphous Si:O:C films synthesized at 200, 300, 400°C by the liquid–solution-phase (LSP) method. The intensity was as strong as that of visible emission band from porous silicon. In all the films, a band existed, centered at 340 nm, while a shoulder band centered at 380 nm was observed from the films deposited at 400°C. By analyzing the PL and photoluminescence excitation (PLE) spectra, Fourier-transform infrared (FTIR) absorption, X-ray photoelectronic spectroscopy (XPS) and X-ray diffraction (XRD), we suggest that the photoluminescence peak at 340 nm originates from the defects in silicon oxide network, while the peak at 380 nm may be related to Si–C and Si–Si bonds in the samples.

Growth of β‐SiC film by pyrolysis of polyimide Langmuir–Blodgett films on silicon

The heteroepitaxial growth of β‐SiC has been studied by pyrolysis of polyimide Langmuir–Blodgett films on silicon substrate in the temperature range 500–1000 °C in vacuum. Thin SiC films have been grown at temperatures above 700 °C. Both the onset temperature of the SiC formation and the growth rate of the SiC films were affected by the orientation of the silicon substrates. The growth rate of the SiC films increased with temperature and was controlled by the reaction of Si with C‐containing reactants. By comparison with dip‐coating polyimide films, it was found that the crystallinity of the SiC layers depended on the degree of order of the molecular arrangement in the polyimide films. Highly ordered superlattice structures of polyimide LB films favored the growth of single crystal SiC films.

Stable ultraviolet photoluminescence from sol–gel silica containing nano-sized SiC/C powder

Abstract PL band of 340 nm has been observed from sol–gel silica with and without the addition of nano-sized SiC/C powder. With the increasing of annealing temperature, the intensity of the 340-nm PL band in pure silica decreases remarkably, while that in SiC/C powder-added silica is enhanced. Based on the Fourier-transform infrared (FTIR) absorption and X-ray photoelectron spectroscopy (XPS) spectra, the authors suggest that the addition of nano-sized SiC/C powder into porous silica (PSO) will strengthen the silica network and prevent it from shrinking during heat treatment. By this mechanism, the 340-nm PL band is stabilized by the presence of SiC/C powder.

SiC formation at the interface of polyimide Langmuir–Blodgett film and silicon

X‐ray photoelectron spectroscopy has been used to explore the process of the interaction between the polyimide film made by the Langmuir–Blodgett method and the substrate Si(111). It is evident that the process includes three stages: The polymer degrades below temperature of about 500 °C resulting in some hydrocarbon species on the surface; at higher temperatures the residual hydrocarbons convert to some state of elemental carbon and then diffuse into the substrate to form ‘‘C–Si alloy’’ which is regarded as a precursor of SiC formation; SiC starts to form at about 700 °C and grows at higher temperatures.