Changshan Xu

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.

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.

Phytotoxic and genotoxic effects of ZnO nanoparticles on garlic (Allium sativum L.): A morphological study

Abstract The effects of zinc oxide nanoparticles (ZnO NPs) on the root growth, root apical meristem mitosis and mitotic aberrations of garlic (Allium sativum L.) were investigated. ZnO NPs caused a concentration-dependent inhibition of root length. When treated with 50 mg/L ZnO NPs for 24 h, the root growth of garlic was completely blocked. The 50% inhibitory concentration (IC50) was estimated to be 15 mg/L. The mitosis index was also decreased in a concentration- and time-dependent manner. ZnO NPs also induced several kinds of mitotic aberrations, mainly consisted of chromosome stickiness, bridges, breakages and laggings. The total percentage of abnormal cells increased with the increase of ZnO NPs concentration and the prolongation of treatment time. The investigation provided new information for the possible genotoxic effects of ZnO NPs on plants.

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...

Single-Phased White-Emitting 12CaO·7Al2O3:Ce3+, Dy3+ Phosphors with Suitable Electrical Conductivity for Field Emission Displays

A novel white-light-emitting phosphor, 12CaO·7Al2O3:Ce3+, Dy3+with H− encaging, was prepared by the solid-state reaction in H2 atmosphere. Upon excitation at 362 nm, the phosphor shows intense white-light emission that combines the blue and yellow emissions at 476 and 576 nm, assigned to the 4F9/2 → 6H15/2 and 4F9/2 → 6H13/2 transitions of Dy3+, respectively. A weak broad blue emission centered at 430 nm is also observed and attributed to the 5d–4f transitions of Ce3+. The photoluminescence intensity of Dy3+ increases greatly with increasing Ce3+ concentration, indicating that the effective energy transfer occurred from Ce3+ to Dy3+ in the phosphor. In particular, the phosphor can be converted to a persistent semiconductor upon ultraviolet irradiation due to the electrons released from the encaged H− ions, and the electrical conductivity is measured to be 10−2 S cm−1. The conductive phosphor exhibits excellent white-light emission (CIE coordinate of (0.324, 0.323)) under low-voltage (5 kV) electron beam excitation, suggesting that the phosphor is a potential candidate for applications in field emission displays.

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...

A multiphase strategy for realizing green cathodoluminescence in 12CaO center dot 7Al(2)O(3)-CaCeAl3O7:Ce3+,Tb3+ conductive phosphor

A multiphase strategy is proposed and successfully applied to make the insulating green phosphor CaCeAl3O7:Tb(3+) conductive in the form of 12CaO·7Al2O3-CaCeAl3O7:Ce(3+),Tb(3+). The phosphor shows bright green-light emission with a short lifetime (2.51 ms) under low-voltage electron beam excitation (3 kV). The green photo- and cathodoluminescence from (5)D4-(7)F(J) (J = 6, 5, 4, 3) transitions of Tb(3+) are significantly enhanced in comparison with pure C12A7:Tb(3+). It was confirmed that this enhancement is the consequence of the joint effects of energy transfer from Ce(3+) to Tb(3+) and broadening of the absorption spectrum of Ce(3+) due to the existence of multiple phases. In particular, under 800 V electron beam excitation, cathodoluminescence is improved by the modified electrical conductivity of the phosphor. When compared to the commercial Zn2SiO4:Mn(2+) with a long luminescence lifetime of 11.9 ms, this conductive green phosphor has greater advantage for fast displays.

Photoluminescence of wurtzite ZnO under hydrostatic pressure

Photoluminescence (PL) spectra of single-crystal ZnO bulk under hydrostatic pressure are studied using the diamond-anvil-cell technique at room temperature. The PL spectrum of ZnO single crystal taken at atmospheric pressure was dominated by a strong near-band-edge exciton emission. The emission line was found to shift towards higher energy with increasing applied pressure. By examining the pressure-dependent PL spectral features, the pressure coefficient of the direct Γ band gap of the wurtzite ZnO was determined. The hydrostatic deformation potential of the band gap has also been deduced from the experimental results.

Pressure-dependent photoluminescence of ZnO nanosheets

Photoluminescence and Raman spectra of ZnO single-crystal nanosheets have been studied as a function of applied hydrostatic pressure using the diamond-anvil-cell technique at room temperature. The ZnO nanosheets synthesized via a vapor transport process have uniform plane surfaces with lateral dimensions up to several microns and thickness of ∼100nm. In terms of Raman results, the ZnO nanosheets underwent a transition from wurtzite to rock-salt structure with an increase of pressure, and the phase-transition pressure was measured to be about 11.2 GPa. However, a strong near-band-edge UV emission of ZnO nanosheets was observed with the applied pressure up to 20.0 GPa. Simultaneously, the emission peak shifted to higher-energy side with increasing pressure. By examining the dependence of the near-band-edge emission peak on the applied pressure, the pressure coefficient of the direct Γ band gap in the wurtzite ZnO nanosheets was determined.