Synthesis and magnetic properties of Cu-doped ZnO nanowire arrays

Spectroscopic properties of Dy3+ doped ZnO for white luminescence applications

Undoped and Dy³⁺ (0.25, 0.5, 0.8 and 1.5at.%) doped ZnO were elaborated by solid-state reaction method. The ZnO:Dy³⁺ samples were characterized using X-ray diffraction (XRD), Raman spectroscopy, UV-vis diffuse reflectance spectroscopy and photoluminescence (PL). The XRD analysis confirms the wurtzite structure of ZnO. A slight shift to lower angles, of the (101) peak, is seen with Dy³⁺ content, indicating the substitution of these ions into the ZnO lattice. Raman study indicates the good crystallinity of all ZnO:Dy³⁺ samples and confirms the substitution of Zn²⁺ by Dy³⁺. The band gap energy was found to increase then decrease with Dy content. The PL excitation spectra (PLE) of Dy³⁺ showed six excitation bands with hypersensitive at 346nm (⁶H_15/2→⁶P_7/2). PL spectra show principally three emission bands relatives to ⁴F_9/2→⁶H_15/2 (476nm), ⁴F_9/2→⁶H_13/2 (567nm) and ⁴F_9/2→⁶H_11/2 (658nm) transitions. The concentration dependency of PL intensity indicates a quenching for Dy³⁺ concentration above 0.5at.%. The PL lifetime of ⁴F_9/2 metastable state was measured and discussed for all Dy content in ZnO. The temperature dependency of PL intensity is investigated for ZnO:Dy (0.5%) sample and the activation energy is determined. The CIE chromaticity color coordinate shows that ZnO:Dy³⁺ can be useful for white luminescence applications.

Cu-doped ZnO nanorod arrays: the effects of copper precursor and concentration

Cu-doped ZnO nanorods have been grown at 90°C for 90 min onto a quartz substrate pre-coated with a ZnO seed layer using a hydrothermal method. The influence of copper (Cu) precursor and concentration on the structural, morphological, and optical properties of ZnO nanorods was investigated. X-ray diffraction analysis revealed that the nanorods grown are highly crystalline with a hexagonal wurtzite crystal structure grown along the c-axis. The lattice strain is found to be compressive for all samples, where a minimum compressive strain of -0.114% was obtained when 1 at.% Cu was added from Cu(NO3)2. Scanning electron microscopy was used to investigate morphologies and the diameters of the grown nanorods. The morphological properties of the Cu-doped ZnO nanorods were influenced significantly by the presence of Cu impurities. Near-band edge (NBE) and a broad blue-green emission bands at around 378 and 545 nm, respectively, were observed in the photoluminescence spectra for all samples. The transmittance characteristics showed a slight increase in the visible range, where the total transmittance increased from approximately 80% for the nanorods doped with Cu(CH3COO)2 to approximately 90% for the nanorods that were doped with Cu(NO3)2.

Synthesis and magnetic properties of Zr doped ZnO Nanoparticles

Zr doped ZnO nanoparticles are prepared by the sol-gel method with post-annealing. X-ray diffraction results show that all samples are the typical hexagonal wurtzite structure without any other new phase, as well as the Zr atoms have successfully entered into the ZnO lattices instead of forming other lattices. Magnetic measurements indicate that all the doping samples show room temperature ferromagnetism and the pure ZnO is paramagneism. The results of Raman and X-ray photoelectron spectroscopy indicate that there are a lot of oxygen vacancies in the samples by doping element of Zr. It is considered that the observed ferromagnetism is related to the doping induced oxygen vacancies.

Synthesis, magnetic anisotropy and optical properties of preferred oriented zinc ferrite nanowire arrays

Preferred oriented ZnFe2O4 nanowire arrays with an average diameter of 16 nm were fabricated by post-annealing of ZnFe2 nanowires within anodic aluminum oxide templates in atmosphere. Selected area electron diffraction and X-ray diffraction exhibit that the nanowires are in cubic spinel-type structure with a [110] preferred crystallite orientation. Magnetic measurement indicates that the as-prepared ZnFe2O4 nanowire arrays reveal uniaxial magnetic anisotropy, and the easy magnetization direction is parallel to the axis of nanowire. The optical properties show the ZnFe2O4 nanowire arrays give out 370-520 nm blue-violet light, and their UV absorption edge is around 700 nm. The estimated values of direct and indirect band gaps for the nanowires are 2.23 and 1.73 eV, respectively.