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.     

Influence of surface modification by 2-aminothiophenol on optoelectronics properties of ZnO nanoparticles

In this study, a precipitation method was used to synthesise ZnO nanoparticles using suitable precursors. An efficient surface modification method was proposed in order to reduce the agglomeration among synthesised small sized ZnO nanoparticles using 2-aminothiophenol as a capping agent. This article briefly investigated the effects of capping agent like 2-aminothiophenol on the optoelectronic properties of ZnO nanoparticles. The modified effectivity of 2-aminothiophenol has been examined on the nanosized ZnO nanoparticle for fluorescence and UV–visible (UV–vis) studies. The mechanism was studied for ZnO nanoparticles light emitting capability under different conditions. By facilitating the capping of ZnO with 2-aminothiophenol, fluorescence emission of the surface defects vanishes and ultraviolet (UV) emission increases. Surface capping by 2-aminothiophenol effectively covers most of the surface defects of ZnO and results in quenching of the visible region. The UV–vis absorption spectra of modified ZnO nanoparticles has been influenced by modified ZnO nanoparticles as a result of surface modification; where marked blue shift in absorption edge results. By surface modification of ZnO nanoparticles, change in optoelectronics properties has opened the new scope and possibilities to explore and fine tune the optical character of the modified ZnO for various optoelectronics applications such as UV laser.     

Synthesis and optical characteristics of ZnO nanocrystals

Zinc oxide nanomaterials with an average particle size of 20–30 nm are readily synthesized by the reaction of zinc acetate and oxalic acid under hydrothermal conditions. The samples are characterized by XRD, SEM, TEM, UV and photoluminescence (PL) studies. The average crystal size of the as prepared ZnO nanopowder is determined by XRD and the values are in good agreement with the TEM analysis. UV absorption spectra revealed the absorption at wavelength < 370 nm indicating the smaller size of ZnO nanoparticles. The quality and purity of ZnO nanomaterial crystalline samples are confirmed by photoluminescence spectra.     

Optical and photoluminescence studies of gold nanoparticles embedded ZnO thin films

Gold nanoparticles (AuNPs) embedded ZnO thin films were prepared by sandwiching a thin thermally evaporated Au film between two sputtered ZnO films. The films were characterized by high resolution transmission electron microscopy (HRTEM), glancing angle X-ray diffraction (GXRD), optical absorption and photoluminescence (PL) measurements. GXRD data exhibited peaks which were attributed to the reflections from various ZnO and Au planes. Size dependence of the plasmon absorption was studied by forming nanoparticles with various sizes. Optical absorption spectra showed strong absorption due to localized surface plasmons at about 608, 638 and 676 nm for films having average AuNPs sizes of 27, 40 and 67 nm respectively. AuNPs embedded ZnO film showed a strong reduction in the intensity of photoluminescence, which was prominent in the case of pure ZnO film. The rise in temperature at a single nanoparticle site was calculated to be 22 K for a particle size of 80 nm.     

Effect of zinc oxide concentration in fluorescent ZnS:Mn/ZnO core–shell nanostructures

In the present work, we have prepared zinc sulphide (ZnS:Mn)/zinc oxide (ZnO) core–shell nanostructures by a chemical precipitation method and observed the effect of ZnO concentration on the fluorescent nanoparticles. Change in the morphological and optical properties of core–shell nanoparticles have been observed by changing the concentration of ZnO in a core–shell combination with optimum value of Mn to be 1 % in ZnS. The morphological studies have been carried out using X-ray diffraction (XRD) and transmission electron microscopy. It was found that diameter of ZnS:Mn nanoparticles was around 4–7 nm, each containing primary crystallites of size 2.4 nm which was estimated from the XRD patterns. The particle size increases with the increase in ZnO concentration leading to the well-known ZnO wurtzite phase which was coated on the FCC phase of ZnS:Mn. Band gap studies were performed by UV–visible spectroscopy and a red shift in absorption spectra have been observed with the addition of Mn as well as with the capping of ZnO on ZnS:Mn. The formation of core–shell nanostructures have been also confirmed by FTIR analysis. Photoluminescence studies show that emission wavelength is red shifted with the addition of ZnO layer on ZnS:Mn(1 %). These core–shell ZnS:Mn/ZnO nano-composites will be a very suitable material for specific kind of tunable optoelectronic devices.     

Rapid synthesis of pure and narrowly distributed Eu doped ZnO nanoparticles by solution combustion method

Pure ZnO:Eu³⁺ nanoparticles (~ 50 nm) were prepared by a solution combustion method. ZnO and Eu₂O₃ were used as starting materials and dissolved in nitric acid. Citric acid was used as a fuel. The reaction mixture was heated at 350 °C resulting into a rapid exothermic reaction yielding pure nanopowders. The atomic weight concentration of Eu³⁺ doped in ZnO was 20%. Transmission electron microscopy (TEM) was used to study the particle size and morphology. The nanopowders were characterized for phase composition using X-ray diffractrometry (XRD). Particle size distribution (PSD) analysis of ZnO: Eu³⁺ showed particle sizes ranging from 30 to 80 nm.The photoluminescence emission spectra of ZnO:Eu³⁺ nanostructures showed a strong band emission around 618 nm when excited with 515 nm wavelength.     

Preparation of monodisperse ZnO/SiO2 composite particles using spray drying with an anionic surfactant template and their photoluminescence characteristics

The photoluminescence (PL) characteristics of ZnO/SiO₂ composite particles were investigated. ZnO/SiO₂ composite particles were synthesized utilizing the consecutive sol–gel spray drying method by incorporating sodium lauryl sulfate (SLS) as a particle morphology control agent. The effect of SLS concentration and ZnO ratio on precursors was studied further on the composite particle morphology and PL performance. Elevating the SLS concentration exhibited a reduction in the particle diameter and an increase in particle uniformity. The particle diameter without SLS was 6.18 µm and reduced to 2.6 µm with the addition of SLS at 3 critical micelle concentrations (CMC). The decrease in ZnO concentration also reduced the particle diameter of the ZnO/SiO₂ composite to 1.74 µm at a ZnO concentration of 25% mol. In addition, the increase in the excitation wavelength from 230 nm to 320 nm indicates a shift in the peak emission intensity at higher wavelengths from 467 nm to 645 nm. The excitation wavelength-dependent photoluminescence phenomenon was exhibited by incorporating silica into the ZnO precursor pre- and post-drying to deliver composite particles. The addition of silica to the composite particles can augment the PL emission intensity without causing a shift in the PL emission peaks when excited at the same wavelength. The 25% mol ZnO composite particles with the addition of SLS 3 CMC had the highest PL emission intensity. The amount of silica nanoparticles sufficient to trap the ZnO nanoparticles in the droplet is an important factor besides the size and uniformity of the particles, which causes the high intensity of PL emission.     

Photoluminescence of Si nanocrystallites and amorphous oxygen-containing si nanoparticles: the reversible effect of ambient atmosphere on luminescence

Si nanocrystallites of various sizes and oxygen-containing Si nanoparticles with different oxygen contents were prepared by vapor condensation. The Si nanocrystallites showed a visible light emission from 500 nm to 900 nm with the peak at 800 nm, and the intensity of photoluminescence increased with decreasing the particle size. This photoluminescence observed in vacuum could be quenched by air and hydrogen, and reappeared after the sample chamber was evacuated. The oxygen-containing Si nanoparticles consisting mainly of Si oxide were amorphous and had an average particle size of approximately 20 nm. Increasing the oxygen content of nanoparticles caused a blueshift of the absorption edge in the transmission spectra. A blue-green photoluminescence with two peaks at 500 nm and 800 nm was observed from these oxygen-containing Si nanoparticles. The luminescence intensity increased with the oxygen content of nanoparticles, and was very sensitive to the ambient atmosphere. Much lower intensity was observed in air, but higher intensity could be recovered in vacuum. Surface states and oxygen-induced luminescent centers were proposed to be responsible for the photoluminescence from the Si nanocrystallites and oxygen-containing Si nanoparticles, respectively. The reversible ambient effect in both cases could be explained by surface charge redistribution during the gas adsorption and desorption processes.     

Small angle X-ray scattering and photoluminescence study of ZnO nanoparticles synthesized by hydrothermal process

Polydisperse ZnO nanoparticles have been synthesized by a hydrothermal process. Small-angle X-ray Scattering (SAXS) was performed for particle size distribution analysis of ZnO nanoparticles. Room-temperature photoluminescence measurements revealed that the ZnO nanoparticles have a single visible emission peak ～600?nm, although polydispersity of the sample shows no presence on PL spectrum. It seems the orange emission ～600?nm is due to the presence of Zn(OH)₂ on the surface of ZnO nanoparticles, instead of the commonly assumed interstitial oxygen defect.     

Impact of layer thickness and light transmission of ZnO nanomaterials on GaN-based light emitting diodes

Highly transparent ZnO nanomaterials have been successfully dispersed in the form of nanoparticles and nanorods on InGaN/GaN-based surface mounted light emitting diodes (SM-LEDs). An effortless spin-coating technique is employed to disperse the ZnO nanoparticle layers, and a well-known hydrothermal technique is used for growing the ZnO nanorods. The layer thickness and the light transmission at a specific wavelength are the major factors in improving the light output power of the devices. Field emission scanning electron microscope (FESEM) images are used to confirm the uniform dispersion of the ZnO nanostructures on the top of the SM-LEDs. The layer thickness and the level of light transmission at 460 nm are examined from the cross-sectional FESEM images and UV absorption spectra, respectively.     

Structural and optoelectronic characterization of prepared and Sb doped ZnO nanoparticles

This paper briefly reports the structural and optoelectronics properties of prepared pure and Sb doped ZnO nanoparticles. Doping with suitable elements offers an efficient method to control and enhance the optical properties of ZnO nanoparticles, which is essential for various optoelectronics applications. Sb doped ZnO nanoparticles have significant concern due to their unique and unusual electrical and optical properties. In the present work, we report the synthesis of Sb doped ZnO successfully with average particle size range from 26 to 29 nm via direct precipitation method. The phase purity and crystallite size of synthesized ZnO and Sb doped nano-sized particles were characterized and examined via X-ray diffraction (XRD) and scanning electron microscopy (SEM). The elemental analyses of undoped and doped ZnO nanoparticles were examined by using energy-dispersive X-ray spectroscopy (EDAX).We investigated and measured the optoelectronics properties of synthesized ZnO and Sb doped ZnO nanoparticles by employing photoluminescence and UV–Visible spectroscopy. The influence of Sb doping on photoluminescence (PL) spectra of ZnO nanoparticles, which consists of UV emission and broad visible emission band, is found to be strongly dependent upon the Sb concentration for all the Sb doped ZnO nanoparticles samples under investigation. The UV–Visible absorption study shows an increase in band gap energy as Sb is incorporated on the ZnO nanoparticles.     

Particle size distribution study by small-angle X-ray scattering technique and photoluminescence property of ZnO nanoparticles

ZnO nanoparticles have been synthesised by thermal decomposition of zinc acetate at ～800°C. The structural characteristics and size distribution of ZnO nanoparticles have been investigated by X-ray powder diffraction (XRD) and small-angle X-ray scattering (SAXS), respectively. SAXS study reveals nanoparticles are of different sizes: namely 23 wt% of 8 nm, 19 wt% of 21 nm and 58 wt% of 51 nm. These ZnO nanoparticles possess yellow visible emission at 552 nm. The polydispersity and single emission peak at 552 nm in ZnO nanoparticles suggest that the yellow emission might be a bulk property instead of having a surface origin in nanostructured ZnO. The surface impurities are characterised by Fourier-transform infrared spectroscopy. The quenching of band edge emission in ZnO nanoparticles seems due to the presence of surface impurities.     

A dual-colored bio-marker made of doped ZnO nanocrystals

Bio-compatible ZnO nanocrystals doped with Co, Cu and Ni cations, surface capped with two types of aminosilanes and titania are synthesized by a soft chemical process. Due to the small particle size (2-5?nm), surface functional groups and the high photoluminescence emissions at the UV and blue-violet wavelength ranges, bio-imaging on human osteosarcoma (Mg-63) cells and histiocytic lymphoma U-937 monocyte cells showed blue emission at the nucleus and bright turquoise emission at the cytoplasm simultaneously. This is the first report on dual-color bio-images labeled by one semiconductor nanocrystal colloidal solution. Bright green emission was detected on mung bean seedlings labeled by all the synthesized ZnO nanocrystals. Cytotoxicity tests showed that the aminosilanes capped nanoparticles are non-toxic. Quantum yields of the nanocrystals varied from 79% to 95%. The results showed the potential of the pure ZnO and Co-doped ZnO nanocrystals for live imaging of both human cells and plant systems.     

Green synthesis of the Ag/ZnO nanocomposite using Valeriana officinalis L. root extract: application as a reusable catalyst for the reduction of organic dyes in a very short time

A facile and green synthesis of the Ag/ZnO nanocomposite by extract of Valeriana officinalis L. root in the absence of any stabiliser or surfactant has been reported in this work. The green synthesised Ag/ZnO nanocomposite was characterised by Field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), energy dispersive X‐ray spectroscopy (EDS), elemental mapping, Fourier‐Transform infrared (FT‐IR), X‐ray diffraction analysis (XRD) and UV‐Vis spectroscopy. According to SEM and TEM images, the Ag and ZnO particles are spherical with diameters of less than 20 and 40–50 nm, respectively. The Ag NPs/ZnO nanocomposite proved to be an effective catalyst in the reduction of various dyes including methyl orange (MO), Congo red (CR) and methylene blue (MB) in the presence of NaBH₄ in aqueous media at ambient temperature. A maximum degradation (100%) of dyes was performed using Ag/ZnO nanocomposite. The extraordinary performance of the prepared Ag/ZnO nanocomposite is attributed to the synergetic effect induced by both ZnO and Ag NPs in the catalytic degradation of organic dyes. The catalyst could be reused and recovered several times with no significant loss of catalytic activity.Inspec keywords: nanocomposites, silver, zinc compounds, II‐VI semiconductors, nanofabrication, catalysts, reduction (chemical), field emission electron microscopy, scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectra, ultraviolet spectra, visible spectra, X‐ray diffraction, surface morphology, nanoparticles, dyesOther keywords: green synthesis, nanocomposite, Valeriana officinalis L. root extract, reusable catalyst, reduction, organic dyes, surfactant, field emission scanning electron microscopy, transmission electron microscopy, energy dispersive X‐ray spectroscopy, elemental mapping, Fourier‐transform infrared spectroscopy, X‐ray diffraction analysis, surface morphology, nanoparticles, methyl orange, congo red, methylene blue, UV–Vis spectroscopy, size 40 nm to 50 nm, wavelength 493 nm, wavelength 465 nm, wavelength 663 nm, Ag‐ZnO     

Enhanced wound healing activity of Ag–ZnO composite NPs in Wistar Albino rats

In the present study, silver (Ag) and Ag–zinc oxide (ZnO) composite nanoparticles (NPs) were synthesised and studied their wound‐healing efficacy on rat model. Ultraviolet–visible spectroscopy of AgNPs displayed an intense surface plasmon (SP) resonance absorption at 450 nm. After the addition of aqueous Zn acetate solution, SP resonance band has shown at 413.2 nm indicating a distinct blue shift of about 37 nm. X‐ray diffraction analysis Ag–ZnO composite NPs displayed existence of two mixed sets of diffraction peaks, i.e. both Ag and ZnO, whereas AgNPs exhibited face‐centred cubic structures of metallic Ag. Scanning electron microscope (EM) and transmission EM analyses of Ag–ZnO composite NPs revealed the morphology to be monodispersed hexagonal and quasi‐hexagonal NPs with distribution of particle size of 20–40 nm. Furthermore, the authors investigated the wound‐healing properties of Ag–ZnO composite NPs in an animal model and found that rapid healing within 10 days when compared with pure AgNPs and standard drug dermazin.Inspec keywords: wounds, tissue engineering, biomedical materials, nanocomposites, nanofabrication, nanomedicine, silver, zinc compounds, II‐VI semiconductors, wide band gap semiconductors, ultraviolet spectra, visible spectra, nanoparticles, particle size, surface plasmon resonance, spectral line shift, X‐ray diffraction, scanning electron microscopy, transmission electron microscopyOther keywords: enhanced wound healing activity, Ag‐ZnO composite nanoparticles, Wistar Albino rats, wound‐healing efficacy, ultraviolet‐visible spectroscopy, intense surface plasmon resonance absorption, aqueous Zn acetate solution, SP resonance band, blue shift, X‐ray diffraction analysis, diffraction peaks, face‐centred cubic structures, scanning electron microscope, SEM, transmission electron microscope, TEM, monodispersed hexagonal nanoparticles, quasihexagonal nanoparticles, particle size, animal model, time 10 d, size 20 nm to 40 nm, Ag‐ZnO     

Structural, optical and photoluminescence studies of heavily Mn-doped ZnO nanoparticles annealed under Ar atmosphere

Undoped and heavily Mn-doped with ZnO nanoparticles (Zn_1?xMn_xO, x?=?0.0, 0.05, 0.1 and 0.2) annealed under Ar atmosphere have been synthesized by a sol–gel method. The structural properties and optical absorption of the prepared samples have been examined by powder X-ray diffraction, energy dispersive X-ray analysis, Fourier transform infrared (FTIR) spectroscopy and UV–visible spectrophotometer. Hexagonal wurtzite structure of the samples is confirmed by the XRD spectra. The average crystalline size of the Zn_1?xMn_xO nanoparticles has been calculated from X-ray line broadening and is decreased from 35.73 to 18.24?nm with increase in Mn concentrations from 0.0 to 0.2. The increase in lattice parameters indicates the substitution of Mn in ZnO lattice. SEM and TEM photographs indicated that the grain size of undoped ZnO is bigger than the Mn-doped ZnO which is due to the limitations of grain growth upon Mn doping. The presence of functional groups and the chemical bonding due to Mn doping is confirmed by FTIR spectra. PL spectra of the Zn_1?xMn_xO system showed that the shift in near band edge emission at 390?nm and a blue band emission at 450–490?nm which confirms the substitution of Mn.     

Influence of Mg doping on the microstructure and PL emission of wurtzite ZnO synthesized by microwave processing

In this paper, we report the synthesis of nano-structured Zinc Oxide (ZnO) and Magnesium doped Zinc Oxide (ZnO:Mg) using air stable and inexpensive chemicals, by microwave assisted processing. The as-synthesized ZnO and ZnO:Mg nanopowders were annealed at 800 °C for 1 h. The samples were further characterized by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy (SEM) and room temperature photoluminescence (PL) spectra. The crystallite size of ZnO decreased from 24 to 16 nm, and the intensity of most prominent vibration band of ZnO becomes weak when Mg dopant is added. SEM images of Mg doped ZnO showed clearly distinct hexagonal shaped nanoparticles with good crystalline quality and size contrast to ZnO. The PL result indicate that the ZnO exhibit strong and sharp UV emission peak at 380 nm. Our result showed that, by doping magnesium into ZnO, the UV emission peak shift towards the lower wavelength at ~370 nm with increasing intensity, which may be attributed to the size confinement. From this study, the microwave processing method has been proved to be successful for preparing other metal oxide nanopowders with good crystal quality.     

Room temperature ferromagnetism in Tb-doped ZnO dilute magnetic semiconducting nanoparticles

Pure and Tb-doped ZnO nanoparticles have been synthesized by chemical co-precipitation method. The transmission electron microscopy study reveals the spherical morphology of synthesized nanoparticles with average particle size 14–18 nm. The effect of Tb-doping on structural, optical and magnetic properties has been studied. X-ray diffraction shows that pure and Tb-ZnO nanoparticles exhibit wurtzite structure having hexagonal phase with primitive unit cell. It further reveals that there is no effect of Tb-doping on the X-ray diffraction pattern up to 2 % doping, however, higher doping concentration result in accumulation of Tb on ZnO surface. Photoluminescence spectra reveal that the doping Tb in ZnO changes crystallographic structure generating non-radiative oxygen vacancies. Three emission peaks located around 423, 485 and 515 nm has been observed. Pure ZnO nanoparticles show diamagnetic character, however, Tb-doped ZnO nanoparticles exhibit room temperature ferromagnetism. The correlation between defects generated upon Tb-doping to the observed ferromagnetism, in the synthesized nanoparticles, has been reported.     

Preparation and characterization of ZnO/ZnS core/shell nanocomposites through a simple chemical method

In this paper, we reported the preparation of ZnO/ZnS core/shell nanocomposites by sulfidation of ZnO nanostructures via a simple hydrothermal method. The precursors of bare ZnO nanoparticles and ZnO nanorods were synthesized by a surfactant-assisted hydrothermal growth. The structural, morphological, and element compositional analysis of bare ZnO nanostructures and ZnO/ZnS core/shell nanocomposites were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, and transmission electron microscopy techniques. The XRD results indicated that the phase of bare ZnO nanoparticles and ZnO nanorods was wurtzite structure, and the phase of coated ZnS nanoparticles on the surface of bare ZnO nanostructures was sphalerite structure with the size of about 8 nm. Photoluminescence measurement was carried out, and the PL spectra of ZnO/ZnS core/shell nanocomposites revealed an enhanced UV emission and a passivated orange emission compared to that of bare ZnO nanostructures. In addition, the growth mechanism of ZnO/ZnS core/shell nanostructures through hydrothermal method was preliminarily discussed.     

A solvothermal route to ZnO and Mn-doped ZnO nanoparticles using the cupferron complex as the precursor

ZnO nanoparticles have been synthesized from the cupferron complex by a solvothermal route in toluene solution. The nanoparticles have been prepared in the presence of various capping agents, of which the best results were obtained with tri-n-octylphosphine oxide, polyethylene glycol, and sodium bis (2-ethylhexyl) sulphosuccinate. The particles obtained with these capping agents have diameters in the 8-14 nm range. The nanoparticles have been characterized by electron microscopy, UV absorption spectroscopy, and photoluminescence spectroscopy, besides x-ray diffraction. Optical spectra of the small nanoparticles show evidence for quantum confinement. ZnO nanoparticles doped with 5% and 10% Mn could be prepared by the solvothermal route starting with a Zn(1-x)Mnx cupferron complex, and the Mn-doped nanoparticles remain paramagnetic down to 5K.