Raghvendra S. Yadav

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.

Photoluminescence and photoconductive characteristics of hydrothermally synthesized ZnO nanoparticles

In the present paper, ZnO nanoparticles (NPs) with particle size of 20–50 nm have been synthesized by hydrothermal method. UV-visible absorption spectra of ZnO nanoparticles show absorption edge at 372 nm, which is blue-shifted as compared to bulk ZnO. Photoluminescence (PL) and photoconductive device characteristics, including field response, light intensity response, rise and decay time response, and spectral response have been studied systematically. The photoluminescence spectra of these ZnO nanoparticles exhibited different emission peaks at 396 nm, 416 nm, 445 nm, 481 nm, and 524 nm. The photoconductivity spectra of ZnO nanoparticles are studied in the UV-visible spectral region (366–691 nm). In spectral response curve of ZnO NPs, the wavelength dependence of the photocurrent is very close to the absorption and photoluminescence spectra. The photo generated current, Ipc = (Itotal - Idark) and dark current Idc varies according to the power law with the applied field IpcαVr and with the intensity of illumination IpcαILr, due to the defect related mechanism including both recombination centers and traps. The ZnO NPs is found to have deep trap of 0.96 eV, very close to green band emission. The photo and dark conductivities of ZnO NPs have been measured using thick film of powder without any binder.

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.

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.

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.

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.

Formation of stable and strong green luminescent ZnO/Cd(OH)2 core-shell nanostructure by sol–gel method

Highly stable and strong green luminescent ZnO/Cd(OH)2 core-shell nanoparticles have been synthesised by simple sol–gel route. X-ray diffraction (XRD) and energy dispersive analysis of X-rays confirm the formation of ZnO/Cd(OH)2 core-shell nanoparticles. The XRD and UV–visible spectroscopy shows that ZnO core size can be efficiently engineered by varying initial precursor ratio. The photoluminescence emission spectra showed the remarkably stable and enhanced visible (green) emission from suspended ZnO/Cd(OH)2 nanoparticles in comparison with bare ZnO nanoparticles. It was postulated that Cd(OH)2 layer at the surface of ZnO nanoparticles prevent the agglomeration of nanoparticles and efficiently assist the trapping of hole at the surface site, a first step necessary for visible emission.

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.

TUNING THE BAND GAP OF ZnO NANOPARTICLES BY ULTRASONIC IRRADIATION

In this present paper, we report the tunability of ZnO nanoparticles by ultrasonic irradiation. Different sized ZnO nanoparticles viz. 2.58–2.97 nm have been synthesized with variation of ultrasonic irradiation time 75–270 min in presence of Histidine as capping agent. UV and visible spectroscopy study revealed that as ultrasonic irradiation time increases, there is increase in amount of formed ZnO nanoparticles and also there is red shift in absorption edge. This confirms the tunability of bandgap of histidine capped ZnO nanoparticles with ultrasonic irradiation. Growth mechanism for controlling the size of ZnO nanoparticles are also discussed.

Histidine functionalised biocompatible CdS quantum dots synthesised by sonochemical method

Histidine functionalised CdS quantum dots (QDs) have been synthesised by sonochemical method. Transmission Electron Microscopy (TEM) observation shows that the histidine functionalised CdS QDs are well-defined, nearly spherical particles. The X-ray diffraction pattern indicates formation of cubic phase of CdS/histidine QDs. The absorption spectra confirm quantum confinement of histidine functionalised CdS QDs. The photoluminescence property of CdS/histidine QDs is found better than that of CdS QDs. Histidine functionalised CdS QDs, in which histidine acts as a biocompatibiliser, can find potential applications in the biological fields.