Optical studies of electrochemically synthesized CdS nanowires

In this paper, electrochemical fabrication and characterization of CdS nanowires having diameter 100 and 200 nm is reported. Nano-channels in anodic alumina membrane were utilized as template. Morphological study of nanowires was made using Scanning electron microscopy (SEM). UV–visible absorption and laser induced time resolved photoluminescence (PL) spectroscopy were used for optical characterization. UV–visible absorption depicts that, there is slight increase in band gap of nanowires with decrease in diameter of nanowires. PL measurements indicate emission band peak of 435 and 420 nm in case of 200 and 100 nm wires respectively. These studies are very important regarding the synthesis and optoelectronic applications of CdS nanowires.     

Quantum confinement effect of CdS nanoparticles dispersed within PVP/PVA nanocomposites

Nanocomposite films of CdS nanoparticles within PVP/PVA blend were prepared. The prepared films were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy, Ultraviolet–visible spectroscopy (UV–vis), transmission electron microscopy (TEM) and photoluminescence (PL) spectra. The amount of Cd⁺ used strongly influenced the size of the CdS nanoparticles, which was confirmed by XRD, UV–vis absorption spectra, PL emission spectra and TEM images. Smaller sized CdS nanoparticles were formed in higher content of cadmium. The results of XRD indicate that CdS nanoparticles were formed with hexagonal phase in the polymeric matrix. PL and UV–vis spectra reveal that nanocomposite films shows quantum confinement effect. Optical band gap and particle size were calculated and is in agreement with the results obtained from TEM data. The direct energy band gap was increased up to 2.86 eV.     

Structural,photoluminescence and picosecond nonlinear optical effect of In-doped ZnO nanowires

In-doped ZnO (IZO) nanowires were grown using the chemical vapour deposition method. The IZO nanowires have been characterized by scanning electronic microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), energy dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), photoluminescence (PL) and UV–Visible spectroscopy. The PL results demonstrated a larger band-gap for the IZO nanowires in comparison to the undoped ZnO. Two major emission peaks were observed for the IZO nanowires, one originated from the free exciton recombination (ultraviolet emission) and another possibly related to the deep-level emission (visible emission). Furthermore, the nonlinear optical characteristic of the nanowires was studied using picosecond Z-scan technique. The experimental results show that the two and three-photon absorption coefficient of samples were able to be observed. These studies make the promising potential applications of the samples in the development of multifunctional all-optical devices.     

Optical properties of ordered ZnO/Ag thin films on polystyrene spheres

A thorough research of the optical properties of ZnO/Ag structures sputtered by RF on PS colloidal crystal molds with different diameters is reported. The influences of the period of the substrates on the performance of ZnO thin films were studied. The results of scanning electron microscopic, X-ray diffraction patterns and UV–vis absorption spectroscopy indicated that the ZnO/Ag thin films were well-covering on PS colloidal crystal molds. The diameter of the polystyrene particles significantly influenced the PL spectrum intensity of ZnO/Ag by affecting the interferences of light. After adding PS colloidal crystal molds with different diameters, all the samples show two luminescent regions, namely a strong, narrow UV emission peak and a wide, weak visible emission band. However, the signal of UV emission increases more significantly. In particular, the maximum enhancement occurs when the diameter is 300 nm. This work proposes an effective way to improve ZnO light emission based on a simple, rapid and cost effective method to fabricate ordered periodic substrates by preparing single layer polystyrene microspheres masks.     

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.     

Synthesis and morphological studies of ZnCuTe ternary nanowires via template-assisted electrodeposition technique

ZnCuTe nanowires have been successfully synthesized via template-assisted one step electrodeposition technique from an aqueous solution of zinc sulphate (ZnSO₄·7H₂O), copper sulphate (CuSO₄·5H₂O) and tellurium oxide (TeO₂) at room temperature (303?K). Nanowires of diameter 200, 100 and 50?nm have been synthesized on copper and indium tin oxide coated glass substrates using track-etch polycarbonate membranes (Whatman). The morphologies and structures of electrodeposited ZnCuTe nanowires were characterized by Scanning electron microscopy (SEM) and X-ray diffraction (XRD). SEM confirmed the formation of nanowires and reveal that the morphologies of nanowires have diameter equal to the diameter of the templates used. The XRD pattern have shown a preferential growth of ZnCuTe nanowires along the (119) direction and the structure corresponding to hexagonal structure. Energy dispersive X-ray analysis confirmed that the zinc copper telluride nanowires are constituted of elements Zn, Cu and Te.     

Formation and characterisation of CeO2 and Gd:CeO2 nanowires/rods for fuel cell applications

Ceria and gadolinium (Gd) doped ceria nanowires have been synthesised by hydrothermal technique with mild reaction conditions. The structure and morphology of as-prepared nanowires were studied by X-ray diffraction and field emission scanning electron microscopy (FE-SEM) techniques. The FE-SEM analysis revealed the formation of nanowires with an average diameter of 10–15 nm. Atomic force microscopy (AFM) analysis for the annealed samples confirms the existence of well defined nanorods of 120–150 nm diameter and 1–1.3 μm length. Fluorescence and diffuse reflectance spectroscopy techniques have been used to study the optical properties of the prepared nanowires. The observed red shift in the ultraviolet–visible absorption spectra confirmed the promoted electron–phonon interaction in CeO₂ and Gd:CeO₂ nanowires compared to bulk structures. The prepared nanowires/rods were thermally stable at up to 350?°C, as revealed by thermogravimetric analysis. The electrical properties were studied by cyclic voltammetry (CV) and impedance spectroscopy. The CV results demonstrated that Gd:CeO₂ exhibited a higher electro-oxidation than CeO₂ nanowires.     

Strong yellow emission of ZnO hollow nanospheres fabricated using polystyrene spheres as templates

ZnO hollow nanospheres were fabricated using polystyrene (PS) microspheres as templates were demonstrated in this paper. The structures and morphologies of obtained products were characterized by XRD, FESEM and TEM. The results revealed that ZnO hollow nanospheres possess a hexagonal wurtzite structure with a diameter around 450–500 nm. Ultraviolet–visible (UV–vis) analysis showed that ZnO hollow nanospheres had high absorption in the ultraviolet region and low absorption in the visible region. Room temperature photoluminescence (PL) spectrum showed a weak UV emission at 380 nm and a strong and broad yellow emission centered at 550 nm. The formation mechanism of hollow structure was also investigated.     

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.     

Structural and photoluminescence investigation of ZnSe nanocrystals dispersed in organic and inorganic matrices

In this work, we report on the investigation of the effect of dispersion of zinc selenide (ZnSe) nanocrystallites into polystyrene (PS) and silica (SiO₂) thin films on their structural, morphological and photoluminescence properties. The ZnSe/PS nanocomposites thin films were synthesized by a direct dispersion of ZnSe crystallites into polymers solution, whereas the ZnSe–SiO₂ films were prepared on glass substrates by the sol–gel dip-coating technique. X-ray diffraction (XRD), Fourier transform infrared spectroscopy, scanning electron microscopy (SEM), energy-dispersive X-rays (EDX), UV–visible spectrophotometry and photoluminescence spectroscopy (PL) techniques have been used to study the structural, morphological and optical properties of the prepared nanocomposite thin films. XRD patterns have demonstrated the incorporation of cubic ZnSe in both organic and inorganic matrices. SEM micrographs have indicated that ZnSe dispersion in the films is homogeneous. UV–visible absorption spectra of the nanocomposite thin films have put into evidence that the dispersion of ZnSe nanocrystals in the thin film matrices improved their optical absorption. Room temperature PL spectra have shown that the addition of ZnSe enhanced the UV emission of PS and all the emission of SiO₂ thin films.     

Shed light on submerged DC arc discharge synthesis of low band gap gray Zn/ZnO nanoparticles: Formation and gradual oxidation mechanism

Synthesis of colloidal metal oxides with controllable size and morphology is burgeoning field of research in nanoscience. Low band gap gray Zn/ZnO colloidal nanoparticles were fabricated by plasma-liquid interaction of DC arc discharge in water. Scanning electron microscopy, X-ray diffraction and UV–vis spectroscopy were employed for morphology, crystal structure and optical characterizations respectively. Optical emission spectroscopy was used to investigate the plasma properties during the synthesis and formation mechanism of nanoparticles. Nanoparticles with different size and shape were fabricated only by adjusting discharge current during synthesis without introducing any chemical agent. Electric discharge current was set to 20, 50, 100 and 150?A during synthesis. Estimated values of plasma excitation energies were 2.41, 2.66, 2.86 and 3.04?eV and diameter size of nanoparticles were 63, 42, 37 and 29?nm for these applied currents respectively. Synthesized nanoparticles were dark gray as prepared and became more transparent gradually getting white color finally. XRD and UV–vis results revealed that the oxidation process was time dependent. The colloidal nanoparticles composed of two metal and metal-oxide phase and white crystalline ZnO was achieved after complete oxidation process. These results provided a flexible and versatile method to synthesize metal oxide nanoparticles with controlled composition.     

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.     

Sol–gel derived N-doped ZnO thin films

N-doped ZnO (NZO) thin films have been prepared by a sol–gel method and their electrical and optical properties have been investigated. The prepared NZO films were p-type, and had excellent electrical properties. They had an optical transparency above 85% in the visible range. The UV absorption edge was red-shifted with increasing N-doping concentration. Two emission bands were observed in the photoluminescence (PL) spectra, with one band located in the UV range and the other band consisting of green luminescence. Both UV and green emissions were enhanced with increasing N-doping concentration.     

Fluorescence spectroscopy of electrochemically self-assembled ZnSe and Mn:ZnSe nanowires

We report room temperature fluorescence spectroscopy (FL) studies of ZnSe and Mn-doped ZnSe nanowires of different diameters (10, 25, 50?nm) produced by an electrochemical self-assembly technique. All samples exhibit increasing blue-shift in the band edge fluorescence with decreasing wire diameter because of quantum confinement. The 10?nm ZnSe nanowires show four distinct emission peaks due to band-to-band recombination, exciton recombination, recombination via surface states and via band gap (trap) states. The exciton binding energy in these nanowires exhibits a giant increase (～10-fold) over the bulk value due to quantum confinement, since the effective wire radius (taking into account side depletion) is smaller than the exciton Bohr radius in bulk ZnSe. The 25 and 50?nm diameter wires show only a single FL peak due to band-to-band electron-hole recombination. In the case of Mn-doped ZnSe nanowires, the band edge luminescence in 10?nm samples is significantly quenched by Mn doping but not the exciton luminescence, which remains relatively unaffected. We observe additional features due to Mn(2+) ions. The spectra also reveal that the emission from Mn(2+) states increases in intensity and is progressively red-shifted with increasing Mn concentration.     

Growth of mane-like ZnS nanostructures by using a two-heating zone-tube furnace: structural characterization and photoluminescence

We have synthesized ZnS nanowires with mane-like branches by thermal evaporation of ZnS powder on the Au-coated Si(100) substrate using a two-heating zone tube furnace. The ZnS powder and the Si substrate were kept at 1,000 and 850 °C, respectively, in a nitrogen atmosphere during synthesis of the ZnS nanostructures. Field emission scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction, and photoluminescence (PL) spectroscopy analyses were performed to investigate the structure, morphology and photoluminescence properties of the products. The axial nanowires grow along the [002] direction and have diameters of 100–200 nm, while on the other hand the branch nanowires grow along the [101] direction and their diameters and lengths are 30–50 and 800–100 nm, respectively. The room temperature PL spectrum with a Gaussian fitting exhibits two visible light emission bands centered at around 397 and 458 nm.     

Synthesis and characterization of copper telluride nanowires via template-assisted dc electrodeposition route

Using polycarbonate track-etch membranes (Whatman), copper telluride (Cu_1.75Te) nanowires of diameter 100 nm and 50 nm have been synthesized electrochemically via template-assisted electrodeposition technique on indium tin oxide (ITO) coated glass from aqueous acidic solution of copper (II) sulphate (CuSO₄·5H₂O) and tellurium oxide (TeO₂) at room temperature (30 °C). Scanning electron microscopy (SEM) reveals the morphology of the nanowires having uniform diameter equal to the diameter of the template used. X-ray diffraction (XRD) pattern showed the structure corresponding to the hexagonal structure of copper telluride and single-crystalline. Using UV–visible spectrometry, the optical band gap of copper telluride nanowires was found to be 3.092 eV for 100 nm and 3.230 eV for 50 nm diameters. The photoluminescence (PL) studies shows higher intensity and broad spectrum in the blue region (450–475 nm) of visible light spectrum.     

Solution-phase synthesis of Au@ZnO core-shell composites

A novel solution-phase method for the preparation of Au@ZnO core-shell composites was described. With this method, the composites were grown without heating that is usually needed in other solution methods. Atomic force microscopy (AFM) results show that the diameter of Au@ZnO core-shell composites is about 10.5 nm. X-ray photoelectron spectroscopy (XPS) was applied to characterize Au@ZnO core-shell composites. The optical properties of Au@ZnO core-shell composites, including UV–vis absorption and photoluminescence (PL), were observed at room temperature.     

Influence of Co-doping on the structural, optical and magnetic properties of ZnO nanoparticles synthesized using auto-combustion method

In the present work, we have interested to understand the influence of cobalt doping on the various properties of ZnO nanoparticles, a series of samples were successfully synthesized using sol–gel auto-combustion method. The effects of Co doping on the structural and optical properties of ZnO:Co nanoparticles were investigated using X-ray diffraction (XRD), scanning electron microscopy, fourier transform infrared (FTIR) spectroscopy, ultraviolet–visible spectroscopy, photoluminescence spectroscopy and vibrating sample magnetometer (VSM). With the sensitivity of the XRD instrument, the structural analyses on the undoped and Co-doped ZnO samples reveal the formation of polycrystalline hexagonal-wurtzite structure without any secondary phase. FTIR spectra confirm the formation of wurtzite structure of ZnO in the samples. The optical absorption spectra showed a red shift in the near band edge which indicates that Co²⁺ successfully incorporated into the Zn²⁺ lattice sites. The room temperature PL measurements show a strong UV emission centered at 392 nm (3.16 eV), ascribed to the near-band-edge emissions of ZnO and defect related emissions at 411 nm (violet luminescence), 449 nm (blue luminescence) and 627 nm (orange-red luminescence), respectively. Magnetic study using VSM reveals that all the samples are found to exhibit room temperature ferromagnetism.     

Electroluminescence microspectroscopy of silicon nanocrystals obtained by Si(+) ion implantation in SiO(2)

Room-temperature electroluminescence (EL) has been measured at both macroscopic and microscopic levels from metal-oxide-semiconductor devices containing silicon nanocrystals (Si-nc) embedded in silicon dioxide (SiO(2)) obtained by high-temperature annealing (1050 and 1100?°C) after Si(+) ion implantation. It is found that spatially integrated (macroscopic) EL is dominated by a near-infrared band centered where the photoluminescence (PL) band of Si-nc (from 700 to 1000?nm) is located. However, on a microscopic scale, EL emission is inhomogeneous, the sample surface exhibiting many visible spots of micron-order diameter. EL spectra from a microscopic surface of ～1?μm(2)(μEL) on visible spots have revealed dominant contributions between ～550 and ～650?nm, attributed to oxide defects. These spectral features rapidly decrease with distance from a bright spot, while lower-intensity near-infrared contributions (750-950?nm) remain unaffected up to relatively large distances before eventually becoming extinct. The macroscopic EL measurements can be explained as a superposition of the μEL and PL spectra. A luminescent mechanism is proposed in which charge carriers mostly tunnel through high-defect-density channels in the oxide, yielding bright visible spots, while Si-nc in these channels and their surroundings contribute to the luminescence by hosting electron-hole recombinations (EL) and/or exhibiting PL due to optical excitation from the nearby visible EL spot.     

C and N doped nano-sized TiO2 for visible light photocatalytic degradation of aqueous pollutants

A facile large scale synthesis of high surface area anatase TiO₂ nano material has been carried out by using the solution combustion synthesis with very widely available urea as fuel. The as-obtained puffy powder of anatase TiO₂ was characterised by X-ray diffraction (XRD), Brunauer–Emmett–Teller surface area analysis, ultraviolet–visible (UV–vis) spectroscopy and X-ray photoelectron spectroscopy (XPS) techniques in order to analyse the structural, optical and surface properties of the synthesised material. Diffuse UV–vis spectroscopic data show a red shift in absorption spectra which may be attributed to the possible energy levels added in between the band edges of TiO₂ due to the C and N doping as confirmed by XPS. Photocatalytic activity of the catalyst was assessed by the photocatalytic degradation of methyl orange under visible light irradiation. The effect of an electron acceptor in order to maximise the electron trapping for further inhibiting exciton recombination and thereby enhancing the oxidation of dyes has also been studied by using peroxomono sulphate(PMS) as the electron acceptor.