Non-catalytic and substrate-free method to titania-doped W18O49 nanorods: growth, characterizations, and electro-optical properties

In the present study, titania-doped (Ti-doped) W₁₈O₄₉ nanorods have been prepared using a modified plasma arc gas condensation technique. Characterizations by field-emission gun scanning electron microscopy, X-ray powder diffraction, high-resolution transmission electron microscopy and high-resolution X-ray photoelectron spectroscopy indicate that the as-prepared nanorods with a single-crystalline monoclinic W₁₈O₄₉ phase are of 20–100 nm in diameter and several micrometers in length. The Raman peaks of the Ti-doped W₁₈O₄₉ nanorods show a red-shift Raman peaks, and an additional green-emission peak at 497 nm is observed in the photoluminescence (PL) spectrum compared to pure W₁₈O₄₉ nanorods. Field-emission (FE) measurements reveal that the turn-on (E _to) and threshold (E _thr) voltages of the Ti-doped W₁₈O₄₉ nanorods are 2.2 and 3.4 V/μm, respectively. A vapor–solid process that does not involve the use of catalyst is proposed for the nanorod growth mechanism. Experimental results show that the additional defects resulting from titania doping are responsible for the enhancement of the optical and FE properties of the pure W₁₈O₄₉ nanorods.     

The sensitivity and dynamic response of field ionization gas sensor based on ZnO nanorods

Field ionization gas sensors based on ZnO nanorods (50–300 nm in diameter, and 3–8 μm in length) with and without a buffer layer were fabricated, and the influence of the orientation of nano-ZnO on the ionization response of devices was discussed, including the sensitivity and dynamic response of the ZnO nanorods with preferential orientation. The results indicated that ZnO nanorods as sensor anode could dramatically decrease the breakdown voltage. The XRD and SEM images illustrated that nano-ZnO with a ZnO buffer layer displayed high c-axis orientation, which helps to significantly reduce the breakdown voltage. Device A based on ZnO nanorods with a ZnO buffer layer could distinguish toluene and acetone. The dynamic responses of device A to the NO _x compounds presented the sensitivity of 0.045 ± 0.007 ppm/pA and the response speed within 17–40 s, and indicated a linear relationship between NO _x concentration and current response at low NO _x concentrations. In addition, the dynamic responses to benzene, isopropyl alcohol, ethanol, and methanol reveals that the device has higher sensitivity to gas with larger static polarizability and lower ionization energy.     

A europium(III) organic ternary complex applied in fabrication of?near UV-based white light-emitting diodes

A β-diketone, 2-acetylfluorene-4,4,4-trifluorobutane-1,3-dione (HAFTFBD), and its three europium(III) complexes, Eu(AFTFBD)₃⋅2H₂O, Eu(AFTFBD)₃(TPPO)₂ and Eu(AFTFBD)₃phen, were designed and synthesized, where TPPO was triphenylphosphine oxide and phen was 1,10-phenanthroline. The complexes were characterized by IR, UV-visible, photoluminescence (PL) spectroscopy and thermogravimetric analysis (TGA). The results show that the Eu(III) complexes exhibit a high thermal stability,and wide and strong excitation bands when monitored at 613 nm. Excited by ∼395 nm near UV light, the complexes emitted strong and characteristic red light due to f–f transitions of the central Eu³⁺ ion, and no emission from the ligands was found. The photoluminescence mechanism of the europium(III) complexes was investigated and proposed as a ligand-sensitized luminescence process. Among the three europium(III) complexes, Eu(AFTFBD)₃phen exhibits the highest thermal stability and the most excellent photoluminescence properties. A bright red light-emitting diode was fabricated by coating the Eu(AFTFBD)₃phen complex onto an ∼395 nm-emitting InGaN chip, and the LED showed appropriate CIE chromaticity coordinates (x=0.66, y=0.33). A white LED with CIE chromaticity coordinates (x=0.32, y=0.32) was prepared with Eu(AFTFBD)₃phen as red phosphor, indicating that Eu(AFTFBD)₃phen can be applied as a red component for fabrication of near ultraviolet-based white light-emitting diodes.     

Characterization and photoluminescence studies of Eu<Superscript>2+</Superscript>-doped BaSO<Subscript>4</Subscript> phosphor prepared by the recrystallization method

Eu doped BaSO₄ was prepared by the recrystallization method and characterization of the material was done by using X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive spectroscopy (EDS) and Fourier transform infrared spectroscopy (FTIR) techniques. From the XRD pattern of Eu doped BaSO₄ compound, it was found that the prominent phase formed was BaSO₄ and traces of other phases were very weak and the result of FTIR spectrum of BaSO₄:Eu shows that the sulfur-oxygen stretch was found at around 1100 cm⁻¹. The room-temperature PL spectra of the Eu doped BaSO₄ sample showed one peak centered at 374 nm, which is the characteristic emission of Eu²⁺ ion. This emission band at 374 nm corresponds to the 4f⁶ 5d→4f⁷ (⁸S_7/2) transitions of Eu²⁺ ions. The excitation spectrum taken at the wavelength 374 nm extends over a wide range of wavelengths from 220–350 nm with a strong peak at around 260 nm. Furthermore, the present sample shows good crystal quality and high photoluminescence sensitivity. Hence our results suggest possible potential applications of Eu doped BaSO₄ phosphor in optoelectronic devices.     

Synthesis, structure and electronic properties of ultranarrow CdS nanorods

We report on the one-step synthesis of ultra narrow wurtzite CdS nanorods using bench top chemical decomposition route. The synthesized CdS nanorods are of 1.8 nm in diameter and show major confinement along the radial dimension, which is well below the exciton Bohr radius of bulk CdS (2.5 nm). Structural and self-assembly properties of nanorods are studied using X-ray Diffraction (XRD) and small angle X-ray scattering (SAXS) measurements, which reveal preferred orientation of the nanorods along <00.2> direction with 2D supercrystalline spatial distribution. The estimated nanorod dimensions from XRD is corroborated with the transmission electron microscopy observations. UV–vis and photoluminescence spectroscopy reveals significant increase in the band gap in comparison to bulk CdS which is further tallied with the simulations using effective mass approximation (EMA). Formation of discrete structure of valence band and conduction band due to strongly quantum confined excitons in the radial direction is evidenced from EMA simulation. Combination of experimental and theoretical approach helps in understanding the structure–property relationship for ultranarrow CdS rods which might lead to nanorod based applications.     

Cadmium sulfide rod-bundle structures decorated with nanoparticles from an inorganic/organic composite

We report a new morphology of wurzite cadmium sulfide with nanoparticles decorated on rod-bundle structures, which were synthesized via calcinations of an inorganic/organic composite at 400 °C in air. The composite was hydrothermally synthesized at 180 °C using thioglycolic acid (TGA) and cadmium acetate as starting materials. The structure, composition, and morphology of the prepared material were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscope, FT-IR spectrometry, photoluminescence spectrometry, and UV–visible spectrometry. Results indicated that the composite could be defined as CdS _0.65/Cd–TGA_0.35. X-ray diffraction revealed that the annealed product is CdS with wurtizite phase. The diameter of the rod is about 150–400 nm and the length from the top to the bottom of the decorated nanoparticle is about 100 nm. The composite showed high intensity of photoluminescence with similar peak position, compared to that of wurtzite CdS, because of the structure defects.     

Eu-doped B2O3–ZnO–PbO glass phosphor powders with?spherical shape and fine size prepared by spray pyrolysis

Eu-doped B₂O₃–ZnO–PbO glass phosphor powders with spherical shape and fine size were directly prepared by spray pyrolysis. The glass phosphor powders prepared at a temperature of 1100°C had broad XRD peak at around 28°. One glass phosphor powder was formed from one droplet at the preparation temperature range from 900 to 1100°C. The mean size of the glass phosphor powders was 0.75 μm. The glass transition temperature (T _g ) of the glass phosphor powders prepared by spray pyrolysis was 378.5°C. The excitation spectrum of the glass phosphor powders prepared at the optimum preparation temperature of 1100°C had bands at 362, 381, 392, 463, 525, and 532 nm. The glass phosphor powders had emission spectra with bands at 579, 614, and 653 nm. The glass phosphor powders with doping concentration of Eu of 7 wt% had the maximum photoluminescence intensity. The glass phosphor layer formed from the glass phosphor powders had high transparencies above 90%.     

Facile synthesis and phase control of copper chalcogenides with different morphologies

A series of stoichiometric and nonstoichiometric copper–chalcogenide nanocrystallines with different morphologies, e.g., extremely high aspect ratio nanofibers (Cu₉S₈), tubular structure (Cu _x S (x=∼1.86–1.96), nanorods (CuS, Cu₃₁S₁₆), platelets (β-CuSe, Cu₃Se₂), rope-like Cu₃Se₂, as well as spherical nanoparticles (Cu₇Se₄, Cu_2−x Se), have been successfully synthesized in 20 vol% water and 80 vol% organic solvents mixture under mild conditions. The products were characterized by various techniques, including X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), electronic diffraction (ED), and high-resolution transmission electron microscopy (HRTEM). The studies of the optical properties revealed that the copper chalcogenides have a wide absorption in the range of about 400–700 nm, with accessional IR band. Systematic studies showed that the mixture of 20 vol% water and 80 vol% organic solvents played a key role in controlling the copper chalcogenides with different morphologies and phases.     

Photoluminescence measurements in the phase transition region of Zn<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Cd<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>S films

Thin films of Zn_1−x Cd _x S (0.1 ≤ x ≤ 0.5) were prepared by using pulsed laser ablation technique on corning glass substrates. Phase transition from cubic to hexagonal in Zn_1−x Cd _x S films is determined by X-ray diffraction analysis. We observed a lowering in the phase transition temperature with increase in the cadmium concentration. Transmission electron microscopy suggests the crystalline nature of thin films with average particle size of 15 nm. The grown Zn_1−x Cd _x S samples show the high peak intensity ratio of the near band edge emission to the defect center luminescence even at room temperature, which indicates the small concentration of complex defects in the samples. Photoluminescence measurement show stoichiometric dependence of the energy band gap and is found to have quadratic dependence on x.     

Structural and photoluminescent properties of Ni doped ZnO nanorod arrays prepared by hydrothermal method

Self-assembled Ni-doped zinc oxide (Zn_1−xNi_xO, x = 0.05, 0.10, 0.15, i.e., ZnNiO, nominal composition) nanorod arrays vertically grown on the ZnO seed layer covered glass along [0 0 1] direction were synthesized by hydrothermal method. Their images and structures have been characterized by scan electron microscope (SEM), X-ray diffraction (XRD) and Raman spectra, showing that Ni doping is beneficial to the formation of ZnO nanorods with hexagonal cross section and the enhancement of ZnO crystal quality. X-ray photoemission spectroscopy (XPS) study further demonstrated that Ni atoms were successfully doped into ZnO lattices. The photoluminescence (PL) spectra of ZnNiO samples show near bandedge emission (NBE) peaks at about 380 nm at a low excitation power and the NBE peak position redshifts while its intensity continuously increases with the increase of Ni doping concentration. With the excitation power increasing, the NBE peak redshifts from 380 nm to about 400 nm for ZnNiO nanorod arrays. The NBE mechanisms for ZnNiO nanorod arrays have been discussed, which is helpful for understanding their room temperature ferromagnetisms.     

Microwave-assisted synthesis of Zn<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Cd<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>S–MWCNT heterostructures and their photocatalytic properties

The multi-walled carbon nanotubes (MWCNTs) wrapped with hexagonal wurtzite Zn _x Cd_1−x S nanoparticles with a uniform and small diameter have been prepared to form Zn _x Cd_1−x S–MWCNT heterostructures by microwave-assisted route using Zn(Ac)₂, Cd(NO₃)₂, and thioacetamide as the reactants_. The heterostructures have been characterized by X-ray powder diffraction, scanning and transmission electron microscopy, high-resolution transmission electron microscopy, photoluminescence (PL) and PL excited lifetime. Despite the analogous size and configuration, the Zn _x Cd_1−x S–MWCNT (x = 0, 0.2, 0.5, 0.8, 1) with different Zn concentration exhibit composition-dependent absorption properties in the visible zone. The PL peak positions of Zn _x Cd_1−x S–MWCNT change gradually from ZnS–MWCNT to CdS–MWCNT. The Zn _x Cd_1−x S–MWCNT shows different photocatalytic activity towards the photodegradation of fuchsin acid under visible light illumination, photocatalytic activity of the Zn _x Cd_1−x S–MWCNT decreases gradually with the increase in the Zn concentration, the Zn_0.2Cd_0.8S–MWCNT possessed the best photocatalytic activity. After recycling thrice, the photocatalysts still have about 85% efficiency.     

Structural,electrical and optical properties of boron doped ZnO thin films using LSMCD method at room temperature

Zn_1−x B _x O (0≤x≤0.04) thin films were deposited by the liquid source misted chemical vapor deposition (LSMCD) method. The thin films were polycrystalline with grain sizes of 16 nm to 22 nm. The structural, optical, and electrical properties were investigated by X-ray diffraction, UV-visible spectrophotometry, Raman spectroscopy, and Hall effect measurement. Also scanning electron (SEM) and atomic force microscopy (AFM) techniques were used in order to determine the morphological and topological characteristics of the films. The optimal result of Zn_1−x B _x O films was obtained at x=0.02, with a low resistivity of ≈10⁻² Ω cm, and a high transmittancy of 85% in the visible light spectrum (300 nm ∼ 800 nm).     

N-doping of pentacene by decamethylcobaltocene

We demonstrate n-type doping of pentacene with the powerful reducing molecule decamethylcobaltocene (CoCp₂^*). Characterization of pentacene films deposited in a background pressure of CoCp₂^* by X-ray photoemission spectroscopy and Rutherford backscattering confirm that the concentration of incorporated donor molecules can be controlled to a level as high as 1%. Ultraviolet photoemission spectroscopy show Fermi level (E _F) shifts toward unoccupied pentacene states, indicative of an increase in the electron concentration. A 1% donor incorporation level brings E _F to 0.6 eV below the pentacene lowest unoccupied molecular orbital. The corresponding electron density of ∼10¹⁸ cm⁻³ is confirmed by capacitance–voltage measurements on a metal–pentacene–oxide–silicon structure. The demonstration of n-doping suggests applications of CoCp₂^* to pentacene contacts or channel regions of pentacene OTFTs.     

Synthesis and photocatalytic activity of polyaniline–TiO<Subscript>2</Subscript> composites with bionic nanopapilla structure

Polyaniline (PANI)–TiO₂ nanocomposites possessing both nano and microscale structures were prepared through a facile hydrothermal route in the presence of PANI. The nanopapilla particles were characterized by scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray analysis, X-ray photoelectron spectra, X-ray diffraction, FTIR spectra, UV–Vis spectroscopy, and N₂ adsorption analysis, etc. The results show that the composites possess both nano and microscale structures. The TiO₂ nanorods are dispersed on PANI with one end fixed to the surface. The photocatalytic properties of the powders were verified by the photodegradation of gaseous acetone under UV (λ = 254 nm) and visible-light irradiation (λ > 400 nm). In fact, the photocatalytic effects exhibited by the composite particles were superior to that of pure TiO₂ and P25 samples. This excellent behavior is attributed to the structural features of PANI–TiO₂ microspheres and the synergistic effect between PANI and TiO₂ which facilitates a larger amount of surface active sites. This in turn causes a faster charge separation and slower charge recombination which results in a more efficient decomposition of gaseous pollutants.     

Controlled synthesis and magnetic properties of nickel phosphide and bimetallic iron–nickel phosphide nanorods

Nickel phosphide (Ni₂P) and bimetallic iron–nickel phosphides [(Fe _x Ni _y )₂P] nanorods were fabricated by a seeded growth strategy. This strategy utilized pre-synthesized Fe₃O₄ nanoparticles as seeds and the thermal decomposition of metal precursors by multiple injections in a solution containing trioctylphosphine and didodecyldimethylammonium bromide (DDAB). The nanorods were characterized by transmission electron microscopy, X-ray diffraction, and magnetic measurements were carried out using superconducting quantum interference device (SQUID). The rod length was tunable, ranging from 10 to 110 nm depending on the number of injections, whereas the diameter of the rods was nearly 6 nm. It was found that the rod size increased with the number of injections under the constant total injection concentration and reaction time. In addition, the effect of the DDAB quantity used as a co-surfactant was studied, which showed that an optimum quantity was required to achieve uniform nanorods. Magnetic characterizations were performed over the two kinds of nanorods to identify their respective magnetic phases. The results demonstrated that the Ni₂P nanorods were defined as a Curie–Weiss paramagnet, whereas the (Fe _x Ni _y )₂P nanorods exhibited superparamagnetic characteristics.     

Structure and magnetic properties of Zn<Subscript>0.9</Subscript>Co<Subscript>0.1</Subscript>O nanorods synthesized by a simple sol–gel method using metal acetylacetonate and poly(vinyl alcohol)

Room-temperature ferromagnetism was observed in Zn_0.9Co_0.1O nanorods with diameters and lengths of ∼100–200 nm and ∼200–1000 nm, respectively. Nanorods were synthesized by a simple sol–gel method using metal acetylacetonate powders of Zn and Co and poly(vinyl alcohol) gel. The XRD, FT-IR and SAED analyses indicated that the nanorods calcined at 873–1073 K have the pure ZnO wurtzite structure without any significant change in the structure affected by Co substitution. Optical absorption measurements showed absorption bands indicating the presence of Co²⁺ in substitution of Zn²⁺. The specific magnetization of the nanorods appeared to increase with a decrease in the lattice constant c of the wurtzite unit cell with the highest value being at 873 K calcination temperature. This magnetic behavior is similar to that of Zn_0.9Co_0.1O nanoparticles prepared by polymerizable precursor method. We suggest that this behavior might be related to hexagonal c-axis being favorable direction of magnetization in Co-doped ZnO and the 873 K (energy of 75 meV) being close to the exciton/donor binding energy of ZnO.     

CdS plume composition and dynamics of neutral species upon ablation with 532 nm laser light

The neutral species present in CdS ablation plumes upon nanosecond 532 nm laser irradiation at a moderate fluence of 0.5–0.75 J cm⁻² have been studied. Neutral Cd _n S _m clusters have been identified, some as large as (CdS)₃₃₋₃₄ (1–2 nm in diameter). The analysis of the dynamics of neutral species shows an expansion with two components that differ both in composition and dynamics. A fast, high kinetic energy component, dominated by S₂ which acquires free-flow conditions at short distances from the target, is followed by a slower component characterized by similar speeds for all species. This slower component shows dynamic features that are expected to favor aggregation processes leading to effective cluster formation.     

Growth mechanism, microstructure and transport properties of Sr1−x La x CuO2 (x=0.10−0.15) thin films

Sr_1−x La _x CuO₂ (x=0.10−0.15) thin films with an infinite-layer type structure were grown on BaTiO₃ buffered (001) SrTiO₃ substrates by pulsed laser deposition (PLD). The evolution of the growth front was monitored, in-situ, by high-pressure reflection high-energy electron diffraction (RHEED), while the surface morphology was analyzed by means of atomic force microscopy (AFM), ex-situ. X-ray diffraction (XRD) was used to determine the evolution of the film structure with deposition and cooling parameters, as well as to study the type and level of epitaxial strain in the Sr_1−x La _x CuO₂ films. The RHEED data showed that the Sr_1−x La _x CuO₂ films grow on BaTiO₃/SrTiO₃ following a 2D or Stranski-Krastanov mechanism, depending on the La doping level. The transition point (critical thickness d _c) from layer-by-layer like (2D) to island (3D) growth depends on the film stoichiometry: decreasing the La doping concentration x from 0.15 to 0.10, the critical thickness d _c increases from ∼45 nm to ∼75 nm. In order to induce superconductivity, the Sr_1−x La _x CuO₂ films were cooled down under reduction conditions. The as-deposited films showed semiconducting or metallic behavior, the resistivity decreasing with increasing La concentration. Post-deposition vacuum annealing resulted in a superconducting transition onset (but no zero resistance down to 4.2 K) only for some of the x=0.15 Sr_1−x La _x CuO₂ films.     

Functionalized CdS nanospheres and nanorods

Functionalized nanoparticles are discussed. Surfaces of CdS:Mn/ZnS core/shell nanospheres (Qdots) were converted from hydrophobic to hydrophilic by growth of a SiO₂ shell. The colloidal dispersion was stabilize by adding a surfactant with a negative surface charge, and a cell-penetrating-peptide, TAT, was attached through a primary amine group. The TAT functionalized Qdots were shown to pass the blood-brain-barrier and luminescence in the infused half of the brain.In addition, nanorods of S²⁻ rich CdS were synthesized by reaction of excess S with Cd precursors in the presence of ethylene diamine. The photoluminescence (PL) peak from the S²⁻ rich CdS nanorods was broad with a maximum at ∼710 nm, which was 40 nm longer in wavelength than the PL peak from Cd²⁺ rich CdS (∼670 nm) nanorods. The influence of surface electron or hole trap states on the luminescent pathway of CdS nanorods were used to explain these shifts in wavelength. Nanocrystals of Au with ∼2 nm diameters were grown on S²⁻ rich surfaces of CdS nanorods. Significant quenching of photoluminescence was observed from Au nanocrystals on CdS nanorods due to interfacial charge separation. Charge separation by Au nanocrystals on CdS resulted in enhanced UV photocatalytic degradation of Procion red mix-5B (PRB) dye in aqueous solution.     

Hydrothermal synthesis and photoluminescent properties of YV1 − xPxO4:Eu3+ (x = 0–1.0) nanophosphors

A simple hydrothermal process has been proposed to systematically synthesize europium-doped yttrium phosphate-vanadates with general formula YV_1 − xP_xO₄:Eu³⁺ (x = 0–1.0). All the YV_1 − xP_xO₄:Eu³⁺ products were characterized by x-ray diffraction (XRD) and transmission electron microscopy (TEM), the results of which revealed they were single-phase tetragonal-structured nanocrystals with diameter of 20 nm and their cell parameter a exhibited a linear relationship with the x value. Photoluminescence (PL) excitation and emission intensities of the products were sensitive to the x value and the change of the PL intensity with x was a wave-like curve which reached the peak at x = 0.4 and 0.8. In addition, the x value had an obvious influence on the (⁵D⁰–⁷F₂)/(⁵D₀–⁷F₁) intensity ratio of Eu³⁺.