Surfactant free hydrothermally derived ZnO nanowires,nanorods, microrods and their characterization

ZnO nanowires, nanorods and microrods have been prepared by an organic-free hydrothermal process using ZnSO₄ and NaOH/NH₄OH solutions. The powder X-ray diffraction (PXRD) patterns reveal that the ZnO nano/microrods are of hexagonal wurtzite structure. The Fourier transform infrared (FT-IR) spectrum of ZnO powder shows only one significant spectroscopic band at around 417 cm^?1 associated with the characteristic vibrational mode of Zn–O bonding. The thickness 75–300 nm for ZnO nanorods and 0.2–1.8 μm for microrods are identified from SEM/TEM images. UV–visible absorption spectra of ZnO nano/microrods show the blue shift. The UV band and green emission observed in photoluminescence (PL) spectra are due to free exciton emission and singly ionized oxygen vacancy in ZnO. Finally, the mechanism for organic-free hydrothermal synthesis of the ZnO nano/microrods is discussed.     

High thermal annealing effect on structural and optical properties of ZnO–SiO2 nanocomposite

The effect of annealing temperature on photoluminescence (PL) of ZnO–SiO₂ nanocomposite was investigated. The ZnO–SiO₂ nanocomposite was annealed at different temperatures from 600 °C to 1000 °C with a step of 100 °C. High Resolution Transmission Electron Microscope (HR-TEM) pictures showed ZnO nanoparticles of 5 nm are capped with amorphous SiO₂ matrix. Field Emission Scanning Electron Microscope (FE-SEM) pictures showed that samples exhibit spherical morphology up to 800 °C and dumbbell morphology above 800 °C. The absorption spectrum of ZnO–SiO₂ nanocomposite suffers a blue-shift from 369 nm to 365 nm with increase of temperature from 800 °C to 1000 °C. The PL spectrum of ZnO–SiO₂ nanocomposite exhibited an UV emission positioned at 396 nm. The UV emission intensity increased as the temperature increased from 600 °C to 700 °C and then decreased for samples annealed at and above 800^°C. The XRD results showed that formation of willemite phase starts at 800 °C and pure willemite phase formed at 1000 °C. The decrease of the intensity of 396 nm emission peak at 900 °C and 1000 °C is due to the collapse of the ZnO hexagonal structure. This is due to the dominant diffusion of Zn into SiO₂ at these temperatures. At 1000 °C, an emission peak at 388 nm is observed in addition to UV emission of ZnO at 396 nm and is believed to be originated from the willemite.     

Cobalt-doped cerium oxide nanoparticles: Enhanced photocatalytic activity under UV and visible light irradiation

CeO₂ nanoparticles (NPs) were synthesized by coprecipitation using cerium(III) nitrate hexahydrate as the precursor and ethanol as the solvent. Different concentration of cobalt-doped cerium oxide NPs (3mol % and 6 mol %) were prepared by adding various concentrations of cobalt chloride to cerium nitrate. The as-synthesized NPs were characterized through X-ray diffraction (XRD) measurements, ultraviolet (UV)–visible spectroscopy, Photoluminescence (PL) spectroscopy, and transmission electron microscopy (TEM). XRD results reveal that the as-prepared CeO₂ NPs had a face-centered cubic structure with crystallite size in the range of 5–8 nm. TEM analyses showed that the CeO₂ NPs and Co-doped CeO₂ NPs had a homogenous size distribution (sizes were within 5–12 nm). Band-edge absorption of CeO₂ NPs redshifted upon increasing the Co concentration as compared to undoped CeO₂ NPs. PL spectra reveal a peak shift of CeO₂ emission upon cobalt doping, which were due to an increase in oxygen defects localized between the Ce4f and O2p energy levels (i.e., via formation of Ce³⁺ states). Photocatalytic degradation of methylene blue in aqueous solution under UV and visible (sunlight) irradiation in the presence of pure CeO₂ NPs and of Co-doped CeO₂ NPs was investigated. The efficiency of photocatalytic degradation of CeO₂ NPs increased with the Co concentration both under UV irradiation and under visible light. Co-doped CeO₂ NPs (6 mol%) showed degradation efficiencies of 98% and 89% at 420 min of exposure to UV irradiation and to visible light, respectively.     

The role of oxidizing agents in the structural and morphological properties of CeO2 nanoparticles

Cerium oxide (CeO₂) nanoparticles with good crystallinity and smooth surface are prepared by chemical precipitation method with different bases (NH₃, NaOH and KOH) using cerium nitrate as a source material. The effect of precipitating agents on the growth of cerium oxide nanoparticles are investigated by Photoluminescence (PL), X-ray diffraction (XRD), Fourier transform-infra red spectroscopy (FTIR), thermo gravimetric–differential thermal analysis (TG-DTA), Scanning electron microscope (SEM), Transmission electron microscope (TEM), and X-ray Photoelectron Spectroscopy (XPS). Cubic fluorite crystallites are detected by XRD pattern with preferred orientation along (1 1 1) direction. PL spectra revealed the presence of a strong and broad emission band at425 nm due to the blue shift in the visible region. The broad band below 700 cm⁻¹ is due to the envelope of the phonon band of metal oxide (Ce–O) network as revealed by the IR spectra. The TG-DTA curves revealed that the total weight loss of the samples is 19.67% when the samples are heated upto 800 °C. SEM images exhibits weakly agglomerated spheroid crystallites are obtained with the typical size in the range 10–50 nm. TEM images display that the particles are nearly spherical and square in shape with diameter 8–12 nm. XPS spectrum confirms the existence of Ce⁴⁺ oxidation states in CeO₂samples.     

Structural characterization of Zn1−xCdxO (0≤x≤0.20) microrods grown by spray pyrolysis

Zn_1−xCd_xO (x= 0.00, 0.05, 0.10, 0.15 and 0.20) thin films were obtained by spray pyrolysis and characterized by XRD, SEM, EDAX and optical measurements. The Zn_1−xCd_xO microrods are in the wurtzite crystallographic phase with (0 0 2) preferred orientation. A narrowing of the fundamental band gap from 3.30 to 3.10 eV was observed with the increasing nominal Cd content up to 20 at% due to the direct modulation of the band gap caused by Cd substitution. The undoped ZnO film showed two emission bands in the spectra: one sharp UV luminescence at ∼382 nm and one broad visible emission ranging from 430 to 600 nm. The sharp peak at ∼382 nm is split into two at 376 and 400 nm upon Cd doping at levels of 5 and 10 at%. However this splitting is not observed in the doped ZnO samples containing 15 at% Cd and more. It should also be mentioned that the broad peak at the range of 430–600 nm has almost disappeared in the films containing 5, 10 and 15 at% Cd.     

Absence of photocatalytic activity in the presence of the photoluminescence property of Mn–ZnS nanoparticles prepared by a facile wet chemical method at room temperature

Mn-doped ZnS nanoparticles (NPs) were prepared with dopants at various concentrations using a facile, simple and inexpensive wet chemical method at room temperature. The physicochemical properties of NPs were characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), ultraviolet-visible absorption spectroscopy (UV–vis) and photoluminescence (PL). XRD analysis confirmed formation of ZnS with zinc blende structure and average crystallite size of about 2 nm. TEM analysis revealed formation of hyperfine NPs with rather good uniformity. The room temperature photoluminescence (PL) spectrum of ZnS:Mn²⁺ exhibited an orange-red emission around 600 nm. The maximum PL intensity was observed for 7.5% Mn doped ZnS. The photocatalytic performance of ZnS:Mn²⁺ was successfully demonstrated for degradation of three different model dyes (i.e. Rhodimine B (Rh. B), Bromocresol Green (BCG) and Bromochlorophenol Blue (BCB)). The results revealed that not only was there a remarkable difference in photocatalytic performance of Mn doped ZnS for all three different dyes at different dopant concentrations but also photocatalytic activity was decreased by Mn doping.     

Bio-fabrication of zinc oxide nanoparticles using leaf extract of curry leaf (Murraya koenigii) and its antimicrobial activities

The present study focused on the development of zinc oxide nanoparticles (ZnO NPs) from the leaf extract of Murraya koenigii where zinc nitrate acts as the precursor. The X-ray diffraction (XRD) analysis showed the crystalline structure, and atomic force microscopy (AFM) showed the morphology of the ZnO NPs to be spherical with an average size of 12 nm. Functional groups of the sample were identified by using Fourier transmission infrared (FT-IR) spectroscopy. Their shape, structure and composition were assessed by Field emission scanning electron microscopy (FE-SEM) and energy dispersive spectroscopy (EDS). The results depicted that synthesized ZnO NPs were moderately stable and hexagonal shape, spherical shape with maximum particle size less than 100 nm. The green-synthesized ZnO NPs had prominent activities against Staphylococcus aureus (14.0±0.50 mm) and followed by Bacillus subtilis (13.8±0.76 mm) at the concentration of 200 µg/mL.     

Photocatalytic degradation of methyl orange and gas-sensing performance of nanosized ZnO

ZnO nanoparticles were synthesized by calcining composites of zinc nitrate and poly(vinyl pyrrolidone) (PVP, molecular weight 30 000) at a mass ratio of 1:2 at 500 °C for 2 h. X-Ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques were used to characterize the as-synthesized ZnO nanoparticles. The particles ranged in size from 30 to 50 nm. Infrared spectra of PVP and the PVP+Zn(NO₃)₂·6H₂O composite revealed coordination between the carbonyl (C=O) of PVP and Zn²⁺ of zinc nitrate, which led to a uniform nanoparticle morphology. The gas-sensing properties and photocatalytic performance of the final product were systematically investigated. The results show that the ZnO nanoparticles exhibit both a high response for ethanol detection and excellent photocatalytic activity for degradation of methyl orange under UV irradiation for 30 min.     

ZnO thin Films with blue emission grown using chemical spray pyrolysis

Photoluminescence in the characteristic blue-green region of the spectrum was emitted by zinc oxide (ZnO) thin films grown by chemical spray pyrolysis. We have been able to optimize spray rate and substrate temperature to obtain ZnO thin films with emission centered at ～383 nm and ～517 nm, respectively. We also observed that Al-doped ZnO films resulted in improved radiative efficiency of the near-band-edge emission; optimized Al-doped spray deposited thin films emitted only blue light.     

Investigation on a source of dominant donor in vanadium-doped ZnO films grown by reactive RF magnetron sputtering

The influences of O₂ gas addition in argon plasma on reactive RF magnetron sputtering deposition of vanadium-doped ZnO (VZO) films were examined. ZnO or VZO films with vanadium concentration of 2 at% were deposited on a quartz substrate. Vanadium doping caused oxygen deficiency in ZnO and formed a large number of zinc interstitials (Zn_i), oxygen vacancies (V_O), and zinc vacancies (V_Zn). Carrier density of VZO decreased from 9×10²⁰ to 9×10¹⁸ cm⁻³ between O₂ partial pressure ratio (α_O2) of 0.6% and 1.0% in spite of the increase in valence number of vanadium. This result suggests that Zn_i is the dominant donor in VZO since Zn_i is a shallow-level defect. Average optical transmittance (T_v) at wavelength between 450 and 800 nm of VZO was 61% while that of ZnO was 82% without oxygen addition. Although the optical transmittance of VZO was largely deteriorated by optical absorption of V_O, T_v of VZO improved by oxygen addition and reached 85% at α_O2 of 1.0% via suppression of V_O formation.     

Defect characterization of Tl4GaIn3Se2S6 layered single crystals by photoluminescence

Photoluminescence (PL) spectra of Tl₄GaIn₃Se₂S₆ layered crystals grown by the Bridgman method have been studied in the energy region of 2.02–2.35 eV and in the temperature range of 16–45 K. A broad PL band centered at 2.20 eV was observed at T=16 K. Variations of emission band has been studied as a function of excitation laser intensity in the 0.1 to 149.9 mW cm⁻² range. Radiative transitions from shallow donor level located at 10 meV below the bottom of conduction band to moderately deep acceptor level located at 180 meV above the top of the valence band were suggested to be responsible for the observed PL band. An energy level diagram showing transitions in the band gap of the crystal was plotted taking into account the results of present work and previously reported paper on thermally stimulated current measurements carried out below room temperature. Analysis of the transmission and reflection measurements performed in the wavelength range of 400–1030 nm at room temperature revealed the presence of indirect transitions with 2.22 eV band gap energy.     

Structure,luminescence and photocatalytic activity of Mg-doped ZnO nanoparticles prepared by auto combustion method

A series of Zn_1−xMg_xO nanoparticles with x=0 to 0.15 were prepared by auto combustion method using citric acid as the fuel and chelating agent. Structure, luminescence and photocatalytic properties were systematically investigated by means of X-ray diffraction, scanning electron microscopy, photoluminescence spectra, ultraviolet–visible absorbance measurement and photochemical reactions etc. The samples retained hexagonal wurtzite structure of ZnO and single phase below x=0.13, and the sizes of the nanoparticles were 60–70 nm. The photoluminescence spectroscopy demonstrated blue shift of ultraviolet emission with increasing Mg doping concentration. Both optical measurements of the as grown and Mg doped ZnO nanoparticles showed that the optical band gap could be modified from ~3.28 eV to 3.56 eV as the Mg content x increased from 0 to 0.13. The photocatalytic activities of the samples were evaluated by photocatalytic degradation of methyl orange, and the results showed that the doping of Mg into ZnO nanoparticles could enhance photocatalytic activity compared to the undoped ZnO nanoparticles, which was attributed to increased band gap and superior textural properties. In addition, according to the PL and photocatalytic studies, the critical doping content of effective Mg in ZnO is up to 0.09.     

Tunable properties of cadmium substituted ZnS nanocrystals

Tailored Zn_1−xCd_xS (x = 0, 0.25, 0.5, 0.75 and 1) nanoparticles, synthesized by co-precipitation method under ultrasonic irradiation, were studied by means of X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared (FTIR), UV–Vis and photoluminescence (PL) spectroscopy measurements. According to the XRD results, substitution of Zn²⁺ by Cd²⁺ ion leads to an increase in the lattice parameters and the average size of zinc blended nanoparticles are in the range of 3–4 nm. Transmission electron microscopy image revealed the formation of nano-sized particles with dimension of 5 nm confirming that the samples are quantum dots. The shift observed in the absorption edges by increasing Cd²⁺ ion substitution is ascribed by the alloying effect but the enhancement of band gap energy compared to that of the corresponding bulk value is attributed to the nanometric grain size and quantum confinement effects. The position and intensity of PL emission peaks are tuned with Cd²⁺/Zn²⁺ ion content.     

The optical properties of rare earth Gd doped ZnO nanocrystals

We present a study of the light emission properties, from UV to blue spectral region, of Gd doped ZnO nanocrystals fabricated by means of a thermal evaporation vapor phase deposition process. The samples were grown from a mixed Zn/Gd source, with a molar percentage of Gd ranging from 0% (pure ZnO) to 5%, 10%, or 15%, in a constant O₂/Ar gas mixture flowing at 500° C. The pure ZnO nanocrystals exhibited a strong and predominant UV emission peaking at 375 nm. Besides the UV emission of ZnO nanocrystals, two strong blue emissions, located at 432 and 397 nm, are observed for the sample doped with 5% Gd. The strong blue emissions are mainly induced by the impurity levels of Gd introduced into the band gap of the ZnO nanocrystals. The UV emission of ZnO decreases as the doping concentration of Gd increases, and the blue emission is replaced by a broad defect emission due to the greater number of defects and impurities, as well as Gd₂O₃ on the surface. The results show that the optical properties of ZnO can be tuned by the doping concentration of Gd.     

Effects of ammonia concentration on property of Cd1−xZnxS films by chemical bath deposition

Cd_1−xZn_xS thin films were grown on soda–lime glass substrates by chemical-bath deposition (CBD) at 80 °C with stirring. All the samples were annealed at 200 °C for 60 min in the air. The crystal structure, surface morphology, thickness and optical properties of the films were studied with transmission electron microscopy (TEM), X-ray diffraction (XRD), scanning electron microscopy (SEM), step height measurement instrument and spectrophotometer respectively. The results revealed that Cd_1−xZn_xS thin films had cubic crystal structure and the intensity of the diffraction peak increased gradually as ammonia concentration rose and the grain size varied from 5.1 to 8.3 nm. All of Cd_1−xZn_xS thin films had a granular surface with some smaller pores and the average granule sizes increased from 92 to 163 nm with an increase in ammonia concentration. The Cd_1−xZn_xS thin films had the highest transmittance with ammonia concentration of 0.5 M L⁻¹, whose thickness was 50 nm and band gap was 2.62 eV.     

Nanotribological properties of ALD-processed bilayer TiO2/ZnO films

TiO₂/ZnO films grown by atomic layer deposition (ALD) demonstrated nanotribological behaviors using scratch testing. TEM profiles obtained an amorphous structure TiO₂ and nanocrystalline structure ZnO, whereas the sample has significant interface between the TiO₂/ZnO films. The experimental results show the relative XRD peak intensities are mainly contributed by a wurtzite oxide ZnO structure and no signal from the amorphous TiO₂.With respect to tribology, increased friction causes plastic deformation between the TiO₂ and ZnO films, in addition to delamination and particle loosening. The plastic deformation caused by adhesion and/or cohesion failure is reflected in the nanoscratch traces. The pile-up events at a loading penetration of 30 nm were measured at 21.8 μN for RT, 22.4 μN for 300 °C, and 36 μN for 400 °C. In comparison to the other conditions, the TiO₂/ZnO films annealed at 400 °C exhibited higher scratch resistance and friction with large debris, indicating the wear volume is reduced with increased annealing temperature and loading.     

Giant piezoelectric effect in GaN self-assembled quantum dots

We observe in strained GaN self-assembled quantum dots grown on an AlN layer, a dramatic modification of the optical emission spectra as the dot size varies. In “large” quantum dots with an average height of 4.1 nm, the photoluminescence (PL) peak is centered at 2.95 eV, nearly 0.5 eV below the bulk GaN bandgap. We attribute this enormous redshift to a giant 5.5 MV cm⁻¹ piezoelectric field present in our dots. Temperature-dependent PL studies reveal the strongly zero-dimensional character of this QD system and are consistent with an intrinsic PL mechanism.     

Influences of annealing temperature on structural,magnetic and optical properties of Zn0.98V0.02O nanoparticles

The Zn_0.98V_0.02O nanoparticles were synthesized by the sol–gel method. The relationship between the annealing temperature (600 °C, 700 °C and 800 °C) and the structural, magnetic and optical properties of the obtained samples was studied. The results showed that Zn ions were partially substituted by V ions. The V doped ZnO nanoparticles annealed at 600 °C and 700 °C were single phase wurtize ZnO structure and they were ferromagnetic at room temperature. On the contrary, the sample annealed at 800 °C had a secondary phase of Zn₃V₃O₈. Therefore it was not saturated even in the field of 10,000 Oe due to the coexistence of ferromagnetic and paramagnetic materials. Photoluminescence results indicated that defects probably were the origin of ferromagnetism in V doped ZnO.     

Effects of defect,carrier concentration and annealing process on the photoluminescence of silicon pn diodes

Silicon pn diodes were fabricated by ion implantation of B and P ions with different doses and subsequent annealing processes. Room temperature photoluminescence (PL) were investigated and the factors affecting the PL intensity were analyzed. Results show that both kinds of pn diodes have PL peak centered at about 1140 nm. Dislocation loops resulted from ion implantation and annealing process may enhance the light emission of silicon pn diode due to its band quantum confinement effect to carriers. The luminescence intensity depends on the carrier concentrations in the implantation region. It should be controlled at the range of 1–6×10¹⁶ cm⁻³. Moreover, the PL intensities of pn diodes with furnace annealing (FA) are higher than those with rapid thermal annealing, and the annealing temperature range for FA is 900–1100 °C.     

Synthesis and characterization of ZnS/ZnO/CdS nanocomposites

Water-soluble ZnS/ZnO/CdS (0.1–0.5 M) nanocomposites were successfully synthesized by the chemical precipitation method in air. X-ray diffraction (XRD), transmission electron microscopy (TEM), ultraviolet–visible (UV–vis), photoluminescence (PL) and thermo gravimetric-differential thermal analysis (TG-DTA) were used to characterize the synthesized products. It is found that the ZnS/ZnO/CdS (0.1–0.5 M) core–shell nanocomposite is cubic and hexagonal mixed structure. TEM results showed the prepared nanocomposites are monodispersed and uniform in size. It is confined within 4.3–5.6 nm range. UV–vis absorption spectra were confined growth process of multi shells on ZnS. It showed a red shift with respect to the shells thickness. Fluorescence measurement showed the emission band which exists in the visible region. Stability and phase transition were identified by TG-DTA analysis. The results show an improved florescence property, indicating their potential applications in biological labeling.