Avinash C. Pandey

Photoluminescence and photoconductivity of ZnS:Mn2+ nanoparticles synthesized via co-precipitation method

Mn(2+) doped ZnS nanoparticles are characterized using UV-vis, photoluminescence and photoconductivity studies. The size of Mn(2+) doped ZnS NPs is estimated to be 2-4nm by X-ray diffraction. UV-vis spectra show a blue shift in absorption edge as compared to bulk counterpart. Photoluminescence spectra indicate that orange luminescence varies with Mn(2+) concentration. The Mn(2+) doped ZnS nanoparticles are found to be photosensitive. The doping of Mn(2+) ions improves the photosensitivity of the ZnS nanoparticles system. The time-resolved rise and decay of photocurrent indicate anomalous behavior during steady state illumination.

Growth mechanism and optical property of ZnO nanoparticles synthesized by sonochemical method.

ZnO nanoparticles have been synthesized by ultrasonic irradiation of an aqueous-alcoholic/aqueous-alcoholic-ethylenediamine (EDA) solutions of zinc nitrate and sodium hydroxide. ZnO nanoparticles possess hexagonal wurtzite structures and they exhibit special photoluminescence properties with a red-shift of 22 nm in UV emission band. It is found that the ultrasonic irradiation time and the solvents both influence the growth mechanism and optical properties of ZnO nanoparticles. The possible growth mechanism of ZnO nanoparticles formation by sonochemical method has been tried to discuss.

Synthesis and characterization of single-crystalline α-MoO3 nanofibers for enhanced Li-ion intercalation applications

High quality, single-crystalline alpha-MoO3 nanofibers are synthesized by rapid hydrothermal method using a polymeric nitrosyl-complex of molybdenum(II) as molybdenum source without employing catalysts, surfactants, or templates. The possible reaction pathway is decomposition and oxidation of the complex to the polymolybdate and then surface condensation on the energetically favorable 001] direction in the initially formed nuclei of solid alpha-MoO3 under hydrothermal conditions. Highly crystalline alpha-MoO3 nanofibers have grown along 001] with lengths up to several micrometres and widths ranging between 280 and 320 nm. The alpha-MoO3 nanofibers exhibit desirable electrochemical properties such as high capacity reversibility as a cathode material of a Li-ion battery.

Growth mechanism and photoluminescence property of flower-like ZnO nanostructures synthesized by starch-assisted sonochemical method.

Flower-like ZnO nanostructures have been synthesized by starch-assisted sonochemical method and the effect of starch and ultrasound on the formation of ZnO nanostructure has been investigated. It is observed that starch and ultrasonic wave both plays a vital role on the growth of ZnO nanostructure. X-ray diffraction (XRD) pattern indicated that the synthesized flower-like ZnO nanostructures were hexagonal. FTIR spectrum confirms the presence of starch on the surface of flower-like ZnO nanostructure. The photoluminescence spectrum of flower-like ZnO nanostructure consists of band-edge emission at 393nm as well as emission peaks due to defects. On the basis of structural information provided by X-ray diffraction (XRD) and morphological information by Scanning Electron Microscopy (SEM), a growth mechanism is proposed for formation of flower-like ZnO nanostructures. Differential Scanning Calorimetry (DSC) of starch in liquid medium confirms that gelatinization is a two step process involving two phases.

Differential Susceptibility of Escherichia coli Cells toward Transition Metal-Doped and Matrix-Embedded ZnO Nanoparticles

Dependence of the antibacterial behavior on ZnO (TM-doped and surface-modified) nanoparticles on Escherichia coli cells has been investigated. ZnO nanoparticles that differ in size, activator ion and in the microenvironment in which these nanoparticles are embedded were used. Comprehensive antibacterial studies of these ZnO nanoparticles owing to their size and surface defects are carried out against E. coli cells. These studies have been carried out both in Luria-Bertani medium and on solid agar medium in the presence and absence of light. The differences in antibacterial effect have been quantified in terms of minimum inhibitory concentration, minimum bactericidal concentration, colony forming unit counts, and qualitatively evaluated by growth curves and disk diffusion tests. The difference in antibacterial activities of the ZnO nanoparticles may be attributed to the enhanced or reduced oxygen vacancies and defect states and could be attributed to the increased or decreased surface defects.

Growth mechanism and optical property of CdS nanoparticles synthesized using amino-acid histidine as chelating agent under sonochemical process

Using amino-acid histidine as chelating agent, CdS nanoparticles have been synthesized by sonochemical method. It is found that by varying the ultrasonic irradiation time, we can tune the band gap and particle size of CdS nanoparticles. The imidazole ring of histidine captures the Cd ions from the solution, and prevents the growth of the CdS nanoparticles. The deviation in the linear relation in between cube of radius of nanoparticles and ultrasonic irradiation time confirms the growth of CdS nanoparticles occur via two process; one is the diffusion process of the reactants as well as reaction at the surface of the crystallite. CdS nanoparticles synthesized using histidine as organic chelating agent have band edge emission at approximately 481 nm and have greater photoluminescence intensity with blue-shift to higher energy due to typical quantum confinement effect.

Alteration of magnetic and optical properties of ultrafine dilute magnetic semiconductor ZnO:Co2+ nanoparticles

Single-phase ZnO:Co(2+) nanoparticles of mean size 2-8 nm were synthesized by a simple co-precipitation technique. X-ray diffraction analysis reveals that the Co-doped ZnO nanoparticles crystallize in wurtzite structure without any impurity phase. The wurtzite structure (lattice constants) of ZnO nanoparticles decrease slightly with increasing Co doping concentration. Optical absorption spectra show an increase in the band gap with increasing Co content and also give an evidence of the presence of Co(2+) ions at tetrahedral sites of ZnO and substituted for the Zn site with no evidence of metallic Co. Initially these nanoparticles showed strong ferromagnetic behavior at room temperature, however at higher doping percentage of Co(2+), the ferromagnetic behavior was suppressed, and antiferromagnetic nature was enhanced. The enhanced antiferromagnetic interaction between neighboring Co-Co ions suppressed the ferromagnetism at higher doping concentrations of Co(2+). Photoluminescence intensity owing to the vacancies varies with the Co concentration because of the increment of oxygen vacancies.

Swift heavy ion induced structural and optical modifications in LiF thin film

Thermally deposited 200 nm polycrystalline films of lithium fluoride (LiF) grown on glass substrates were irradiated with 150 MeV Ag ions at various fluences between 1 × 1011 and 2 × 1013 ions cm−2. The irradiation induced structural and optical modifications were studied using glancing angle x-ray diffraction (GAXRD), optical absorption and photoluminescence (PL) spectroscopy. The GAXRD results show that the films are polycrystalline and the average grain size (estimated from the widths of the GAXRD peak using the Scherrer formula) decreases systematically from 46.3 nm for the pristine sample to 18.3 nm for the sample irradiated at a fluence of 3 × 1012 ions cm−2. Thereafter, it remains constant. This reduction is attributed to strain induced fragmentation of grains. The optical absorption studies show dominant absorption bands of F3 (385 nm) and F2 (445 nm) colour centres. It is observed that the concentration of the colour centres increases with ion fluence and gets saturated at higher fluences. This can be correlated with GAXRD results in the sense that as the density of grain boundaries increases the concentration of colour centres also increases. The variation with fluence in PL intensities of the F2 and colour centres is studied. The intensity of both bands (F2 and ) increases up to a fluence of 1 × 1012 ions cm−2, followed by an exponential decrease, which is due to the increase in the non-radiative transition rate in the presence of defect-rich material.

Relationship between oxygen defects and the photoluminescence property of ZnO nanoparticles: A spectroscopic view

The present paper deals with the synthesis and characterization of ZnO nanoparticles obtained by coprecipitation method at three different pH conditions. Samples characterizations aimed at understanding their spectroscopic properties are carried out using a variety of experimental techniques. X-ray diffraction and transmission electron microscopic studies show significant increase in the particle size of the synthesized ZnO nanoparticles ranging from 3–40 nm with increasing pH values. Absorption spectra show particle size dependent blueshift in the energy band, which may be ascribed to quantum confinement effect. Fourier transform infrared (FTIR) spectroscopy reveals enhancement in the surface defects of the synthesized ZnO nanoparticles with increasing pH values. Electron paramagnetic resonance studies at room temperature (300 K) and several liquid helium temperatures (including the lowest temperature 13 K for all samples) indicate the presence of singly ionized oxygen vacancy defects (VO+) and O2− super...

Application of ZnO nanoparticles in influencing the growth rate of Cicer arietinum

In this work, ZnO nanoparticles (NPs) have been synthesised by hydrothermal method. This hydrothermally synthesised product has been characterised by powder X-ray diffraction and field emission scanning electron microscopy (FE-SEM) for the study of crystal structure and morphology/size. FE-SEM image revealed that ZnO NPs are spherical in shape with a diameter of 20–30 nm. The photoluminescence study of these NPs revealed that ZnO NPs consist of three emission peaks at 401, 482 and 524 nm. The UV emission peak at 401 nm is the band edge emission; however, the blue-green emission at 482 nm and green emission at 524 nm is related to defects. These ZnO NPs are used during the seed germination and root growth of Cicer arietinum. The effect of ZnO NPs has been observed on the seed germination and root growth of C. arietinum seeds. The effect of these ZnO NPs on the reactivity of phytohormones, especially indole acetic acid (IAA) involved in the phytostimulatory actions, is also carried out. Due to oxygen vacancies, the oxygen deficient, i.e. zinc-rich ZnO NPs increased the level of IAA in roots (sprouts), which in turn indicate the increase in the growth rate of plants as zinc is an essential nutrient for plants.