C. L. Shao

White-light emission of polyvinyl alcohol∕ZnO hybrid nanofibers prepared by electrospinning

Polyvinyl alcohol∕ZnO (PVA∕ZnO) hybrid nanofibers were prepared by the electrospinning technique. The structural and spectral information of the nanofibers was characterized by scanning electron microscopy, x-ray diffraction, Fourier transform infrared spectroscopy, differential scanning calorimetry, resonant Raman, and photoluminescence (PL). The results indicate that ZnO were successfully embedded in the one-dimensional hybrid fibers via chemical interactions between ZnO and PVA. PL results show the PVA∕ZnO nanofibers have an intense white-light emission, which originates from the simultaneous emission of three bands covering from the UV to visible range. A possible PL mechanism was proposed accordingly.Polyvinyl alcohol∕ZnO (PVA∕ZnO) hybrid nanofibers were prepared by the electrospinning technique. The structural and spectral information of the nanofibers was characterized by scanning electron microscopy, x-ray diffraction, Fourier transform infrared spectroscopy, differential scanning calorimetry, resonant Raman, and photoluminescence (PL). The results indicate that ZnO were successfully embedded in the one-dimensional hybrid fibers via chemical interactions between ZnO and PVA. PL results show the PVA∕ZnO nanofibers have an intense white-light emission, which originates from the simultaneous emission of three bands covering from the UV to visible range. A possible PL mechanism was proposed accordingly.

Optical properties of ZnO and ZnO:In nanorods assembled by sol-gel method

Self-assembled zinc oxide (ZnO) and indium-doping zinc oxide (ZnO:In) nanorod thin films were synthesized on quartz substrates without catalyst in aqueous solution by sol-gel method. The samples were characterized by x-ray diffraction (XRD), scanning electron microscope (SEM), Raman-scattering spectroscopy, room-temperature photoluminescence (PL) spectra, and temperature-dependent PL spectra measurements. XRD and Raman spectra illustrated that there were no single In2O3 phase in ZnO lattice after indium doping. The PL spectra of ZnO showed a strong UV emission band located at 394 nm and a very weak visible emission associated with deep-level defects. Indium incorporation induced the shift of optical band gap, quenching of the near-band-edge photoluminescence and enhanced LO mode multiphonon resonant Raman scattering in ZnO crystals at different temperatures. Abnormal temperature dependence of UV emission integrated intensity of ZnO and ZnO:In samples is observed. The local state emission peak of ZnO:In samples at 3.37 eV is observed in low-temperature PL spectra. The near-band-edge emission peak at room temperature was a mixture of excitons and impurity-related transitions for both of two samples.

F-doping effects on electrical and optical properties of ZnO nanocrystalline films

F-doped and undoped ZnO nanocrystalline films were prepared from thermal oxidation of ZnF2 films deposited on a silica substrate by electron beam evaporation. The F-doped ZnO film has very low electrical resistivity of 7.95×10−4Ωcm and a high optical transmittance. The study also indicated that (1) the substitutional F atoms in the film serve as donors to increase the carrier concentration and the optical band gap with respect to undoped ZnO film, and (2) F passivation reduces the known number of Os2−/Os− surface states and increases carrier mobility.

Room-temperature ferromagnetism in (Mn, N)-codoped ZnO thin films prepared by reactive magnetron cosputtering

(Mn, N)-codoped ZnO films were grown on fused silica substrates by reactive magnetron cosputtering. X-ray diffraction measurements reveal that the films have the single-phase wurtzite structure with c-axis preferred orientation. X-ray photoelectron spectroscopy studies indicate the incorporation of both divalent Mn2+ and trivalent N3− ions into ZnO lattice. Acceptor doping with nitrogen partly compensates the “native donors,” which results in a low electron concentration of 3.16×1016cm−3 though p-type conductivity is not achieved. (Mn, N)-codoped ZnO films show significant ferromagnetism with Curie temperature above 300K. The mechanism of ferromagnetic coupling in codoped ZnO is discussed based on a bound magnetic polaron model.

The structural and optical properties of Cu2O films electrodeposited on different substrates

Cuprous oxide films were successfully electrodeposited onto three different substrates through the reduction of copper lactate in alkaline solution at pH = 10. The substrates include indium tin oxide film coated glass, n-Si wafer with (001) orientation and Au film evaporated onto Si substrate. The substrate effects on the structural and optical properties of the electrodeposited films are investigated by in situ voltammetry, current versus time transient measurement, ex situ x-ray diffraction, scanning electron microscopy, UV–vis transmittance and reflectance and photoluminescence techniques. The results indicate that the choice of substrate can strongly affect the film morphology, structure and optical properties.

Structural and optical properties of ZnO nanotower bundles

ZnO nanotower bundles have been grown on the electrochemically deposited ZnO thin film by a simple hydrothermal process. The influence of surface/interface defects on the structural and optical properties is studied by x-ray diffraction, selected area electron diffraction, and photoluminescence techniques. The formation of ZnO nanotowers and defects may be attributed to kinetic confinement and thermodynamic processes. A wide visible emission band covering nearly the entire visible region is related with the surface/interface defects. By controlling the surface area-to-volume ratio and the width change of the single ZnO nanotower, the emission properties of ZnO nanotowers can be well modified.

Structural, optical, and magnetic properties of Mn-doped ZnO thin film

The Zn(1-x)Mn(x)O (x = 0, 0.16, and 0.25) thin films were grown on fused quartz substrates by reactive magnetron cosputtering. X-ray-diffraction measurement revealed that all the films were single phase and had wurtzite structure with c-axis orientation. As Mn concentration increased in the Zn(1-x)Mn(x)O films, the c-axis lattice constant and band-gap energy increased gradually. In Raman-scattering studies, an additional Mn-related vibration mode appeared at 520 cm(-1). E(2H) phonon line of Zn(1-x)Mn(x)O alloy was broadened asymmetrically and redshifted as a result of microscopic structural disorder induced by Mn(2+) random substitution. The Zn(0.84)Mn(0.16)O film exhibited a ferromagnetic characteristic with a Curie temperature of approximately 62 K. However, with increasing Mn concentration to 25 at. %, ferromagnetism disappeared due to the enhanced antiferromagnetic superexchange interactions between neighboring Mn(2+) ions.

Preparation and characterization of ZnO particles embedded in SiO2 matrix by reactive magnetron sputtering

ZnO particles embedded in SiO2 thin films were prepared by a radio-frequency magnetron sputtering technique. X-ray diffraction (XRD) and optical-absorption spectra showed that ZnO particles with hexagonal wurtzite structure had been embedded in the SiO2 matrix, and the size of ZnO particles increased with increasing annealing temperature from 773to973K. Raman-scattering and Fourier transform infrared (FTIR) spectrum measurements also confirmed the presence of ZnO particles. When the annealing temperature was lower than 973K, room-temperature photoluminescence (PL) spectra showed dominative deep-level emissions in the visible region and very weak ultraviolet emissions. As the annealing temperature increased to 973K, an emission band in the ultraviolet region besides the emissions from free and bound excitons recombination was observed in the low-temperature PL spectra. The origin of the ultraviolet emission bands was discussed with the help of temperature-dependent PL spectra. When the annealing temperatur...

Photoluminescence study of ZnO nanotubes under hydrostatic pressure

Photoluminescence of ZnO single crystal nanotubes grown on sapphire substrate by metal organic chemical vapor deposition has been studied as a function of applied hydrostatic pressure using the diamond-anvil-cell technique. The photoluminescence spectra of the ZnO nanotubes at atmospheric pressure are dominated by strong near-band-edge ΓFX and ΓBX excitonic emission lines accompanied by a weak broad deep-level (DL) emission band. The pressure-induced shifts of all observed emission lines are followed up to 15Gpa, when ZnO nanotubes undergo a phase transition from a direct-gap wurtzite structure to an indirect-gap rocksalt structure. The ΓFX emission is found to shift toward higher energy with applied pressure at a rate of 29.6meV∕GPa, which provides a method to measure the pressure coefficient of the direct Γ band gap in the wurtzite ZnO nanotubes. The ΓBX emission has a pressure coefficient of 21.6meV∕GPa, about 30% smaller than that of the ZnO band gap, which suggests that it might originate from the ra...

Photoluminescence properties of highly dispersed ZnO quantum dots in polyvinylpyrrolidone nanotubes prepared by a single capillary electrospinning

Highly dispersed ZnO quantum dots (QDs) in polyvinylpyrrolidone (PVP) nanotubes have been prepared by a single capillary electrospinning. The structure and optical properties characterizations were performed by x-ray diffraction, scanning and transmission electron microscopy, absorption, photoluminescence, and resonant Raman spectra. In the composites, PVP molecules passivate the surface defects of ZnO QDs and prevent the aggregations of ZnO QDs. As a result, the composites exhibit narrower band edge emissions and less laser thermal effects. Blueshifted band gap, enlarged exciton energy, and less exciton-longitudinal optical (LO) phonon interaction due to the quantum confinement effect have also been observed.