Solvothermal synthesis of hexagonal ZnO nanorods and their photoluminescence properties

Pure hexagonal ZnO nanorods were synthesized by low-temperature (90 °C) solvothermal treatment of zinc acetate in 40-80 wt.% hydrazine hydrate aqueous solutions. The products were characterized by means of powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electronic microscopy (TEM), selected area electron diffraction (SAED), and room temperature photoluminescence (RTPL) spectra. They show a strong UV emission at around 380 nm upon excitation at 360 nm using a Xe lamp at room temperature. The influence on the quality of the nanorods was investigated while the content of the solvent changed. The as-synthesized ZnO nanorods are promising materials for nanoscale optoelectronic devices due to their excellent UV emission properties.     

Simple air oxidation synthesis and optical properties of S-doped ZnO microspheres

The S-doped ZnO microspheres with average diameter of 3 micrometers (μm) have been successfully synthesized by a simple air oxidation process of ZnS precursor. X-ray diffractometer (XRD) pattern indicates that the as-obtained sample is composed of ZnO and ZnS. The scanning electron microscopy (SEM) image shows that the exterior surfaces of the microspheres are composed of many nanoparticles with an average grain size of 100 nanometers (nm). The photoluminescence (PL) spectra show the broad excitation region with the main peak at 370 nm and strong green emission centered at 500 nm, which can be attributed to the oxygen vacancies caused by S replacement of O.     

Microwave-assisted hydrothermal synthesis and optical property of Co3O4 nanorods

Single crystalline Co₃O₄ nanorods have been successfully synthesized through thermal decomposition of the precursor, which was obtained by the microwave-assisted hydrothermal route. The obtained sample was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectrometer (FT-IR), and X-ray photoelectron spectroscopy (XPS). The results confirm that the resulting oxide was pure single-crystalline Co₃O₄ nanorods. The optical property test indicates that the absorption peak of the nanorods shifts towards short wavelength. And the blue shift phenomenon might be ascribed to the quantum effect.     

The evolution of optical properties during hydrothermal coarsening of ZnS nanoparticles

Nearly monodisperse 3-nm ZnS nanoparticles capped with the mercaptoethanol were prepared in aqueous solution. During hydrothermal coarsening of ZnS nanoparticles, the evolution of optical properties and growth kinetics were investigated. As the particle size increased, the absorbance spectrum continued a size-dependent shift to long wavelength. A significant enhancement in photoluminescence was obtained during the growth, indicating the decrease of defects and the increase of ZnS crystallinity. The average particle size and size distribution were calculated from the absorption spectra, which revealed two-stage growth kinetics of ZnS nanoparticles.     

Solvothermal synthesis and photoluminescence properties of ZnO nanorods and nanorod assemblies from ZnO2 nanoparticles

Without the use of any extra surfactant or template, hexagonal phase ZnO crystallites consisting of individual nanorods or nanorod assemblies were synthesized simply by solvothermal treatment of several nanometer ZnO₂ nanoparticles in three different solvents (including ethanol, 80 wt.% hydrazine hydrate aqueous solution and ethylenediamine) at 150 °C for 24 h. The structures and optical properties of the resultant products were characterized by means of X-ray powder diffraction (XRD), scanning electron microscope (SEM), and room temperature photoluminescence (RTPL) spectra. The RTPL spectra of the resultant products all showed a much stronger ultraviolet bandgap emission peaking at around 387 nm and a weaker emission associated with the defect level. The as-synthesized ZnO crystallites are promising materials for the optoelectronic devices due to their excellent UV emission properties.     

Raman study of surface optical phonons in hydrothermally obtained ZnO(Mn) nanoparticles

Nanocrystalline samples of ZnO(Mn) were synthesized by hydrothermal method. The morphology of the samples was studied by HRTEM and SEM. X-ray diffraction was used to determine composition of the samples (ZnO and ZnMn₂O₄) and the mean crystalline size (from 16 to 99 nm). In this paper we report the experimental spectra of Raman scattering (from 100 to 1600 cm⁻¹) with surface optical phonons (SOP) in range of 497–538 cm⁻¹ as well as formation of new phases MnO, Mn₃O₄ and ZnMnO₃. The phonon of registered phase's exhibit effects connected to phase concentration, while the SOP phonon mode exhibit significant confinement effect.     

Synthetics of ZnO nanostructures by thermal oxidation in water vapor containing environments

Metallic Zn films deposited on glass were wet or dry oxidized at 390 °C in pure N₂ or O₂ to understand the effects of water vapor in different oxygen partial pressure on growth of ZnO nanostructure during thermal oxidation. As-prepared ZnO oxides were characterized by a scanning electron microscope (SEM), an X-ray diffractometer (XRD), and a transmission electron microscope (TEM). Optical and electric properties of these ZnO films were characterized by photoluminescence (PL) and resistance measurements, respectively. It was found that the oxygen partial pressure and water vapor of environment significantly affect the morphologies of ZnO nanostructures. Decreasing oxygen partial pressure in dry oxidation can enhance a green light peak at 500 nm on PL spectra arising from defect-related emission and reduce the resistivity of the oxide films. High H₂O^(g)/O₂ ratio in wet oxidation will significantly increase the intensity of a green light peak and reduce the resistivity of the oxide films. The effect of oxygen partial pressure and H₂O^(g)/O₂ ratio on the PL spectra and resistivity of ZnO films are explained by the theory of defects equilibrium during oxidation.     

Synthesis and cathode luminescence properties of ZnO multipod nanoneedles

Zinc oxide (ZnO) multipod nanoneedles over a large area have been synthesized on silicon substrate by thermally oxidizing zinc foil at 650 °C. These nanoneedles have sharp tails with diameter down to less than 100 nm, with length of 10 μm, growing from the surface of the silicon substrate and legs connected at a common base. X-ray diffraction (XRD) confirmed the sample as pure ZnO nanostructures with growth direction of [002]. The cathode luminescence behaviors at different regions of an individual nanoneedle of these multipod ZnO nanostructures were characterized. It is shown the whole nanostructures are luminescent, while the tips have relative higher visible emission than the bottom. The cathode luminescence mechanisms were also discussed.     

Green hydrothermal synthesis and optical absorption properties of ZnO2 nanocrystals and ZnO nanorods

A green hydrothermal method was proposed for the controllable synthesis of ZnO₂ nanocrystals and ZnO nanorods, using the common and cost-effective 2ZnCO₃·3Zn(OH)₂ powder and 30 mass% H₂O₂ aqueous solution as the raw materials. The characterization results from X-ray diffraction, high resolution transmission electron microscopy, transmission electron microscopy and energy dispersive X-ray spectroscopy indicated that the products synthesized at 100-120 °C for 6 h or at 170 °C for 0 h were cubic phase ZnO₂ nanocrystals; while those synthesized at 170 °C for 3-6 h were hexagonal phase ZnO nanorods. The UV-vis absorption spectra showed that the as-synthesized ZnO₂ nanocrystals and ZnO nanorods had optical band gaps of about 4.1 and 3.3 eV, respectively.     

Influence of Ni doping on magnetic behavior of Mn doped ZnO

Enhancement in room temperature ferromagnetism has been observed in Mn doped ZnO, when co-doped with Ni. In the co-doped system, Ni-O-Ni and Ni-O-Mn carrier mediated exchange interaction dominates the Mn-O-Mn exchange interaction which causes a fair increase in the value of saturation magnetization at room temperature. It is believed that the simultaneous doping of Ni and Mn onto ZnO increases the carrier concentration in form of clusters of oxygen vacancies and hence favors the carrier mediated exchange interaction for the enhancement of magnetic moments in the system.     

Optical properties and characterization of zinc nitride nanoneedles prepared from ball-milled Zn powders

Zinc nitride nanoneedles (ZNNs) with diameters at stem and tip parts as 200-300 nm and 30-70 nm respectively have been prepared by the nitridation of ball-milled zinc powders at 600 °C for 120 min under NH₃ gas environment. The structural, compositional and morphological characterizations of the product were conducted by X-ray diffraction, energy dispersive X-ray spectroscopy, scanning electron microscopy and transmission electron microscopy. From transmission spectrum data, an indirect band gap of 2.72 eV has been calculated for ZNNs whereas photoluminescence studies exhibited a strong UV excitonic mission band at 395 nm as well as two weak defect related blue emissions at 453 and 465 nm. A vapor-solid (VS) process based growth mechanism for the formation of ZNNs has also been discussed briefly.     

Raman optical properties of Cu(OH)2 nanowires

We have for the first time investigated Raman optical properties of polycrystalline Cu(OH)₂ nanowires with an average diameter of ca. 9 nm and lengths of up to hundreds of micrometers that were synthesized by a simple surfactant-free solution-phase route at ambient temperature. The result indicated that the Raman peak of the as-prepared polycrystalline Cu(OH)₂ nanowires was obviously broadened, and red-shifted 16 cm^− 1 compared with that of bulk Cu(OH)₂ crystals. Based on the microstructure analysis and phonon confinement model of a crystal, we have proposed a rational explanation for the red-shift and broadening of Raman peak.     

Synthesis of Ni nanoparticles by reduction of NiCl2 ionic clusters in the confined space of AOT reversed micelles

Stable Nickel nanoparticles have been synthesized by a novel synthetic route based on the reduction of NiCl₂ ionic clusters in the confined space of reversed micelles. The reaction was carried out by adding anhydrous NaBH₄/ethanol solution to a solution of NiCl₂ ionic clusters nanoencapsulated in bis(2-ethylhexyl)sulfosuccinate (AOT) reversed micelles in the presence of n-dodecylmercaptane as capping agent. As highlighted by FT-IR, an extraction with water eliminates surfactant and side products leaving lipophilic Nickel nanoparticles to be dispersed in the organic solvent. UV-Vis investigation ascertained the formation of stable metal Nickel nanoparticles exhibiting novel optical properties.     

Piezoelectric, dielectric, optical and electrical characterization of solution grown flower-like ZnO nanocrystal

Flower-like ZnO nanocrystals were grown by low temperature solution technique after controlling Zn²⁺/OH⁻ ratio. The morphology and structural studies confirmed the formation of nano structure, revealing the [0001] oriented growth of the ZnO nanorods. The variation of dielectric constant, loss, ac conductivity and activation energy as a function of frequency was studied. In UV-Vis absorption spectra, a sharp absorption band-edge at 355 nm is observed from which direct optical band gap 3.40 eV was calculated. In P-E hysteresis piezoelectric characterization for unpoled ZnO, the value of remnant polarization and coercive field was found to be 16.31 µC/cm² and 6.11 kV/cm respectively which increased to 25.65 µC/cm² and 8.35 kV/cm, respectively after poling at 1 kV/cm. The piezoelectric charge coefficient (d₃₃) was found to be 1.7 pC/N.     

Structural and optical properties of Al-doped SnO2 nanowires

We report a facile thermal evaporation method for the syntheses of Al-doped SnO₂ nanowires using Al-doped SnO₂ nanoparticles as precursors. High-density, single-crystalline Al-doped SnO₂ nanowires were directly grown on the 6H-SiC substrates without any catalyst. X-ray diffraction patterns show that the Al dopants are incorporated into the rutile SnO₂ nanowires. The X-ray photoelectron spectra confirm the SnO₂ nanowires doped with 5 at.% Al. The photoluminescence spectra of the Al-doped SnO₂ nanowires exhibit that the large blue shift of the emission band can be observed in the Al-doped SnO₂ nanowires compared with undoped nanowires. The distortion of the crystal lattices caused by incorporation of Al atoms at the interstitials should be responsible for the large blue shift of the emission band.     

X-ray photoelectron spectroscopy of silver nanoparticles in phosphate glass

Phosphate glasses doped with silver nanoparticles have been characterized by X-ray photoelectron spectroscopy. A study on the relation of Ag binding energies with the optical properties of the nanocomposites has revealed binding energies for 3d doublets higher than those reported for bulk silver with a tendency towards the bulk value with increasing wavelength of surface plasmon resonance peak position. The data is interpreted in terms of quantum confinement effects in small silver clusters and an increase in particle size with plasmon absorption redshift.     

Facile synthesis of superparamagnetic Fe-doped ZnO nanoparticles in liquid polyols

A facile polyol process was established to prepare superparamagnetic Fe-doped ZnO nanoparticles in a liquid polyol using Fe(acac)₃ and Zn(acac)₂ as precursors and triethylene glycol as the solvent. Scanning electron microscopy (SEM) images showed that as-prepared nanoparticles are uniform in size. X-ray diffraction (XRD) analysis revealed that the nanoparticles are of wurtzite structure without an impure phase. The successful doping of the Fe element into the ZnO host was evident by XRD lines shifting and energy dispersive X-ray spectroscopy (EDS) results. Magnetization measurements demonstrated that the Fe-doped ZnO nanoparticles were superparamagnetic at room temperature.     

Synthesis, characterization and optical properties of sheet-like ZnO

Sheet-like ZnO with regular hexagon shape and uniform diameter has been successfully synthesized through a two-step method without any metal catalyst. First, the sheet-like ZnO precursor was synthesized in a weak alkaline carbamide environment with stirring in a constant temperature water-bath by the homogeneous precipitation method, then sheet-like ZnO was obtained by calcining at 600 °C for 2 h. The structures and optical properties of sheet-like ZnO have been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), photoluminescence (PL) and UV-vis-NIR spectrophotometer. The results reveal that the product is highly crystalline with hexagonal wurtzite phase and has appearance of hexagon at (0 0 0 1) plane. The HRTEM images confirm that the individual sheet-like ZnO is single crystal. The PL spectrum exhibits a narrow ultraviolet emission at 397 nm and a broad visible emission centering at 502 nm. The band gap of sheet-like ZnO is about 3.15 eV.     

Synthesis and luminescence properties of YVO4:Eu nanocrystals grown in nanoporous glass

We report on a feasible method to synthesize luminescence nanocrystals in porous glass in this paper. Well dispersed YVO₄:Eu nanocrystals were proved being grown in nanoporous glass by XRD, micro-Raman spectra and HRTEM equipped with EDS. The YVO₄:Eu³⁺ nanocrystal grown in porous glass herein shows very different luminescence properties compared with single Eu-doped sample. By this method, intense red emission from high silica glass due to energy transfers VO₄³⁻ → Eu³⁺ was obtained. The results show that the reduction from Eu³⁺ to Eu²⁺ in porous glass impregnated with Eu³⁺ ions was avoided effectively.     

Low temperature synthesis and optical properties of CaTiO3 nanoparticles from Ca(NO3)2·4H2O and TiO2 nanocrystals

Choosing low-melting-point Ca(NO₃)₂·4H₂O and high-reactive-activity TiO₂ nanocrystals as the raw materials, a simple and cost-effective route was developed for the synthesis of CaTiO₃ nanoparticles at 600 °C, which is much lower than that (about 1350 °C) used in the conventional solid state reaction methods. X-ray diffraction, energy dispersive X-ray spectroscopy and field emission scanning electron microscopy revealed the formation of orthorhombic phase CaTiO₃ nanoparticles with oxygen-deficiency at the surface. UV-vis absorption spectrum of the as-obtained CaTiO₃ nanoparticles displayed an absorption peak centered at around 325 nm (3.8 eV), together with a tail at lower energy side. Room temperature photoluminescence spectrum of the as-obtained CaTiO₃ nanoparticles upon laser excitation at 325 nm demonstrated a strong and broad visible light emission ranging from about 527 to 568 nm, which may be originated from the surface states and defect levels.