Thermal annealing induced structural and optical properties of Ca doped ZnO nanoparticles

In this letter, the effects of annealing on structural and optical properties of Ca doped ZnO nanoparticles have been investigated. X-ray diffraction analysis reveals that the prepared particles are in hexagonal wurtzite structure and formation of secondary phase related to the Calcite was found after thermal annealing. UV–Vis measurements show free exciton absorption band appeared at 372 nm and increase of band gap with annealing of samples. Room temperature photoluminescence (PL) spectrum of the prepared Ca doped ZnO nanoparticles shows bands which belong to the near band edge emission at 377 nm and green emission at 556 nm. Annealed samples exhibit enhancement in the blue emission band. Raman spectra show the increment in the electron–phonon coupling value with annealing.     

Co^2＋掺杂ZnO纳米线的制备与光学特性的研究

在十六烷基三甲基溴化铵表面活性剂辅助下,通过水热合成法制备了Co2 掺杂ZnO纳米线.纳米线的直径为100～160nm,长度约为10μm.纳米线沿(001)方向生长.Co2 掺杂ZnO纳米线紫外-可见(UV-vis)吸收光谱曲线,显示掺杂的ZnO纳米线在200～300nm波段之间都有很强的紫外吸收,在波长360～370nm处显示很好的激子吸收,与体相的激子吸收峰(373nm)相比产生了蓝移.纳米线分别在385、409、433、462和495nm波段表现出发光特性,简略的讨论了其发光机制.     

Hydrothermal synthesis and optical properties of Pb2+ doped ZnO nanorods

Single-crystalline Pb²⁺ doped ZnO nanorods were synthesized by a hydrothermal method in the presence of cetyltrimethyl ammonium bromide (CTAB). The obtained Pb²⁺ doped ZnO nanorods were in diameters of ∼150 nm and in lengths of ∼3 μm. The nanorods grow along the [011¯0] direction. The Pb²⁺ doped ZnO nanorods show violet and blue emission bands centered at 415, 438 and 467 nm, respectively. The possible growth mechanism of the Pb²⁺ doped ZnO nanorods was also discussed.     

Synthesis, self-assembly, and properties of Mn doped ZnO nanoparticles

We report here a novel process to prepare Mn doped ZnO nanoparticles by a soft chemical route at low temperature. The synthesis process is based on the hydrolysis of zinc acetate dihydrate and manganese acetate tetrahydrate heated under reflux to 160-175 degrees C using diethylene glycol as a solvent. X-ray diffraction analysis reveals that the Mn doped ZnO crystallizes in a wurtzite structure with crystal size of 15-25 nm. These nano size crystallites of Mn doped ZnO self-organize into polydisperse spheres in size ranging from 100-400 nm. Transmission Electron Microscopy image also shows that each sphere is made up of numerous nanocrystals of average diameter 15-25 nm. By means of X-ray photoelectron spectroscopy and electron spin resonance spectroscopy, we determined the valence state of Mn ions as 2+. These nanoparticles were found to be ferromagnetic at room temperature. Monodisperse porous spheres (approximately 250 nm) were obtained by size selective separation technique and then self-assembled in a closed pack periodic array through sedimentation with slow solvent evaporation, which gives strong opalescence in visible region.     

Magnetic, optical and structural studies on Ag doped ZnO nanoparticles

The influences of annealing effects have been explored on the crystallinity, morphology, optical and magnetic properties of Ag–ZnO nanostructures prepared by a simple sol–gel method. X-ray powder diffraction, scanning electron microscope, high resolution transmission electron microscope (HRTEM), vibrating sample magnetometer and photoluminescence spectroscopy (PL) have been used to characterize the crystal structures, surface morphology, magnetic and optical properties of the pure ZnO and Ag–ZnO nanostructures respectively. The synthesized Ag–ZnO nanostructures are found to have hexagonal wurtzite crystal structures and their grain size increases while lattice strain decreases on annealing. From HRTEM observation, it is found that the annealed samples show nanorod like structures with Ag nanoparticles (NPs) embedded on the surface. Due to annealing effect, Ag–ZnO shows higher saturation magnetization at room temperature.     

Structural, optical, photo catalytic and antibacterial activity of ZnO and Co doped ZnO nanoparticles

A systematic investigation on the structural, optical, photo catalytic and antimicrobial properties of pure and cobalt doped ZnO nanoparticles synthesized by Co-precipitation method is presented. X-ray diffraction analysis of these samples showed the formation of phase pure nanoparticles with wurtzite ZnO structure. Optical studies showed a blue shift in the absorbance spectrum with increasing the doping concentration. The Methylene Blue (MB) decomposition rate of the synthesized pure ZnO and cobalt doped ZnO nanoparticles were studied under the UV region. In the UV region, synthesized pure ZnO and cobalt doped ZnO decomposed Methylene Blue (MB). However, the MB decomposition rate obtained using pure ZnO was much higher than that by doped ZnO. The antibacterial property test was carried out via disk diffusion method, and the result indicated antibacterial activity of the prepared samples.     

Investigation on structural,optical and dielectric properties of Co doped ZnO nanoparticles synthesized by gel-combustion route

We report the synthesis of Co doped ZnO nanoparticles by combustion method using citric acid as a fuel for 0%, 1%, 3%, 5% and 10% of Co doping. The structural, optical and dielectric properties of the samples were studied. Crystallite sizes were obtained from the X-ray diffraction (XRD) patterns whose values are decreasing with increase in Co content up to 5%. The XRD analysis also ensures that ZnO has a hexagonal (wurtzite) crystal structure and Co²⁺ ions were successfully incorporated into the lattice positions of Zn²⁺ ions. The TEM image shows the average particle size in the range of 10–20 nm for 3% Co doped ZnO nanoparticles. The energy band gap as obtained from the UV–visible spectrophotometer was found gradually increasing up to 5% of Co doping. The dielectric constants (?′, ?″), dielectric loss (tan δ) and ac conductivity (σ_ac) were studied as the function of frequency and composition, which have been explained by ‘Maxwell Wagner Model’.     

Size-controlled synthesis and optical properties of doped nanoparticles prepared by soft solution processing

In this review, we outline the synthesis and luminescence properties of metal-ion-incorporated doped nanoparticles and surface-passivated doped nanoparticles. The synthetic routes we describe are limited to those involving soft solution processing. The doping effects are discussed in this review on the semiconductor nanoparticles confining the size range near to the 'quantum dot size.' The effects on luminescence with respect to ionic valance of dopants and the luminescence phenomena on mismatching of ionic radii between the host-guest are also provided. In addition, we discuss the role of passivated organic surfactants and the necessity of surface passivation of doped or undoped nanoparticles with other semiconductor materials that possess larger band gaps. Biocompatible semiconductor nanoparticles and some of their applications are also mentioned briefly.     

High-yield chemical synthesis of hexagonal ZnO nanoparticles and nanorods with excellent optical properties

Large yield and low temperature growth of nanostructures are key requirements for fulfilling the demand of large scale applications of nanomaterials. Here, we report a highly efficient chemical method to synthesize high quality hexagonal ZnO nanoparticle and nanorods utilizing the low temperature oxidation of metallic zinc powder in the presence of an appropriate catalyst. This one-step method has advantages such as low temperature (90 degrees C) and atmospheric pressure synthesis and a high yield (> 90%). Microstructure and optical properties of the as-synthesized ZnO nanoparticles are found to be identical or better than those of the commercial ZnO nanopower (Sigma-Aldrich). In particular, in comparison to the commercial nanopowder the as-grown ZnO nanorods and nanoparticles exhibit stronger UV absorption at 376 nm and intense UV photoluminescence emission at -382 nm, with negligible defect emission band. This method is suitable for large-scale production of nanosized ZnO and could be extended for the synthesis of other metal oxides.     

Structural and optical properties of nitrogen doped ZnO films

Zinc oxide is getting an enormous attention due to its potential applications in a variety of fields such as optoelectronics, spintronics and sensors. The renewed interest in this wide band gap oxide semiconductor relies on its direct high energy gap (E_g ∼ 3.437 eV at low temperatures) and large exciton binding energy. However to reach the stage of device production the difficulty to produce in a reproducible way p-type doping must be overcome.In this study we discuss the structural and optical properties of ZnO films doped with nitrogen, a potential p-type dopant. The films were deposited by magnetron sputtering using different conditions and substrates. The composition and structural properties of the films were studied combining X-ray diffraction (XRD), Rutherford backscattering (RBS), and heavy ion elastic recoil detection analysis (HI-ERDA). The results show an improvement of the quality of the films deposited on sapphire with increasing radio-frequency (RF) power with a preferentially growth along the c-axis. The ERDA analysis reveals the presence of H in the films and a homogeneous composition over the entire thickness. The photoluminescence of annealed samples evidences an improvement on the optical quality as identified by the well structured near band edge recombination.     

Stability and nonlinear optical properties of ZnO nanoparticles

Photoluminescence (PL) of ZnO nanoparticles of different surface states and sizes grown by several methods has been measured. The origin of luminescence and dependence of the luminescence spectrum shape and intensity on 325 nm excitation laser power are studied. Strong ultraviolet emission at 3.26 eV, weak violet emission around 3.12 eV and weak green emission at 2.40 eV have been observed in 16 nm nanoparticles capped by octylamine grown by non-hydrolytic method. The nanoparticles are stable under high power laser radiation and their PL intensity increases nonlinearly with an increasing laser power. As the nanoparticle size decreases to 12 nm, high power laser produces nonradiative centers which may quench the luminescence in a degree. Nanoparticles of 8 nm capped by PVP and uncapped nanoparticles of 14 nm are unstable and their luminescence depends on the excitation laser power. High power laser can quench O vacancy emission and enhance ultraviolet emission in PVP capped nanoparticles while vacancy emission can not be quenched in uncapped nanoparticles.     

Sol-gel synthesis,structural and enhanced photocatalytic performance of Al doped ZnO nanoparticles

In this research ZnO and Zn_1?x Al_xO (x = 1, 3, 5, 7% mol) nanoparticles were synthesized by sol-gel method. The effect of Al concentration on the structure, morphology, absorption spectra and photocatalytic properties investigated by using X-ray, TEM, EDS and UV–Vis spectrophotometer approaches. Hexagonal, spherical and rod-like structure was achieved as the dominant structure for undoped nanoparticles, low and high concentrations of doped Al, respectively. Photocatalytic activity of nanoparticles was measured by degradation of methyl orange as a pollutant under radiation of ultraviolet (UV). The experimental test results indicate that the best photocatalytic performance is at of 5% of Al. Furthermore, the doped ZnO nanoparticles have more activity in visible area compared with undoped nanoparticles. The absorption amount in this area increases by raising the Al concentrations. Furthermore, the band gap of the particles decreases from 3.22 eV to 2.93 eV by increasing Al percentage.     

Synthesis,structural and optical properties of Ag doped ZnO nanoparticles with enhanced photocatalytic properties by photo degradation of organic dyes

In present paper chemical route based synthesis of Ag doped ZnO nanoparticles (NPs) by co-precipitation method is reported to develop ZnO NPs for photo catalytic application. XRD confirms the structural purity of ZnO NPs. FESEM and TEM study reveals the surface and ultra structure morphology of NPs. EDAX study confirms the purity and homogeneity of NPs. The Ag/ZnO NPs with different weight percentage of Ag relative to ZnO were applied under visible light irradiation for evaluating heterogeneous photo catalytic degradation of methylene blue (MB) and Brilliant blue (BB) respectively. The presence of Ag in ZnO enhance MB and BB dye degradation effectiveness from 96.78 to 98.66 and 82.15 to 97.36% for pure ZnO and maximum Ag doped ZnO (x?=?0.1) respectively. In comparison of MB and BB final degradation ability, MB dyes have more effective photo catalytic efficiency towards different oxidizing species to degradation process.     

Template-free solvothermal synthesis of ZnO nanoparticles with controllable size and their size-dependent optical properties

ZnO nanoparticles (NPs) have been synthesized via a facile and template-free solvothermal method. The size of ZnO NPs could be tailored by adjusting the ratio of ethanol to ethylene glycol (EG). Their structure and morphology have been investigated. The as-prepared samples are monodispersed ZnO NPs with controllable sizes of about 24.2, 18.9 and 14.7 nm. The cathodoluminescence (CL) spectra of the samples show that the relative intensity ratio of the visible emission peak at 500-650 nm to the band-edge UV emission peak at 380 nm increases as the particle size decreases. Sample with smaller crystallites would have larger surface area and more oxygen vacancy defects, thus it exhibits higher visible emission peak. The UV-vis absorption spectrum indicates the band gap variation of the ZnO NPs with their size. Moreover, the size-dependent blue shifts of both the CL emission and the UV-vis absorption spectra reveal the effect of quantum confinement.     

Physical and magnetic properties of (Co, Ag) doped ZnO nanoparticles

Undoped and (Co, Ag) co-doped ZnO nanostructure powders are synthesized by chemical precipitation method without using any capping agent and annealed in air ambient at 500 °C for 1 h. Here, the Ag concentration is fixed at 5 mol% and Co concentration is increased from 0 to 5 mol%. The X-ray diffraction studies reveal that undoped and doped ZnO powders consist of pure hexagonal structure and nano-sized crystallites. The novel Raman peak at 530 cm^?1 has corroborated with the Co doped ZnO nanoparticles. Moreover, the PL studies reveal that as the Co doping concentration increases and it enters into ZnO lattice as substitutional dopant, it leads to the increase of oxygen vacancies (Vo) and zinc interstitials (Zn_i). From the magnetization measurements, it is noticed that the co-doped ZnO nanostructures exhibit considerably robust ferromagnetism i.e. 4.29 emu g^?1 even at room temperature. These (Co, Ag) co-doped ZnO nanopowders can be used in the fabrication of spintronic and optoelectronic device applications.     

Magnetic and optical properties of Mn doped ZnO nanocrystalline films

We have investigated the properties of Mn-doped ZnO nanocrystalline film growing on zinc foil by the hydrothermal method. X-ray photoelectron spectroscopy shows that the manganese ions exist as Mn2+ in the film. From UV-vis spectra, we observe a red shift in wavelength of absorption and greater reflectivity due to the Mn ion incorporation in ZnO lattices. The photoluminescence spectrum of the Mn-doped ZnO film shows two strong new blue peaks centered at 424 nm and 443 nm, besides the UV emission peak owing to the band gap of ZnO semiconductor. The magnetic property of the Mn-doped ZnO exhibits a room temperature ferromagnetic characteristic with a saturation magnetization (Ms) of 0.3902 x 10(-3) emu/cm3 and a coercive field of 47 Oe. We suggest that the blue emission of the Mn-doped ZnO film corresponds to the electron transition from the level of interstitial Zn and Mn to the valence band. The defects brought about by Mn ion incorporation are the main cause of the room temperature ferromagnetic property.     

Sonochemical synthesis of nitrogen doped ZnO nanorods: effect of anions on growth and optical properties

Sonochemical synthesis of nitrogen doped zinc oxide (ZnO:N) nanorods using acetate and nitrate of the starting materials is reported. X-ray diffraction studies reveal the formation of hexagonal wurtzite phase of ZnO in both the cases whereas the crystallite size is found to be greater in acetate route. Precursor dependent growth process is observed as the time period for precipitation is found to be different with different starting materials. Electron microscopic studies show the formation of rod like structures of ZnO and ZnO:N in both acetate and nitrate routes. But, high aspect ratio and uniformity in the morphology of ZnO:N nanorods is observed in acetate route. High resolution images and selected area diffraction patterns of ZnO:N illustrate the nanorods to be c-axis oriented in both the cases. But in nitrate medium, the growth along [0001] direction is affected due to the adsorption of NO₃ ^? ions onto polar Zn²⁺ surface leading to smaller length of the nanorods. FTIR studies also support these results showing the existence of sharp N–O symmetric stretching in ZnO:N in nitrate route. Photoluminescence (PL) measurements show red shift of excitonic emission band for ZnO in acetate route.     

Study of structural and optical properties of Ge doped ZnO films

The Ge doped ZnO films were deposited on quartz substrates by radio frequency magnetron sputtering. The effects of doping and substrate temperature on the structural and optical properties of the Ge doped ZnO films were investigated by means of X-ray diffraction (XRD), UV-visible transmission spectra, X-ray photoelectron spectroscopy and photoluminescence (PL) spectra. The XRD patterns showed that Zn₂GeO₄ phases were formed in the films. With the increase of substrate temperature the crystallization of Zn₂GeO₄ was improved, and that of ZnO phases turned worse, and no diffraction peak of ZnO was observed when the substrate temperature was 700 °C. Obvious ultraviolet (UV) light emission was found due to ZnO grains, and it was much stronger than that of un-doped ZnO films. The enhancement of UV light emission at about 380 nm may be caused by excitons which were formed at the interface between Zn₂GeO₄ and ZnO grains. In the visible region of the PL spectra, the green light emission peak of samples at about 512 nm was associated with defects in ZnO. A red shift of the green light emission peak was observed which can be explained by the fact that there is a luminescence center at about 548 nm taking the place of the defect emission of ZnO with the increase of substrate temperature. The red shift of the green light emission peak and the 548 nm green light emission peaks of the PL spectrum show that some Ge²⁺ should replace the Zn²⁺ positions during the Zn₂GeO₄ grains growth and form the Ge²⁺ luminescence centers in Zn₂GeO₄ grains.