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Synthesis of core @ shell (Au @ Ag) nanoparticle with varying silver composition has been carried out in aqueous poly vinyl alcohol (PVA) matrix. Core gold nanoparticle (~15 nm) has been synthesized through seed-mediated growth process. Synthesis of silver shell with increasing thickness (~1-5 nm) has been done by reducing Ag over the gold sol in the presence of mild reducing ascorbic acid. Characterization of Au @ Ag nanoparticles has been done by UV-Vis, High resolution transmission electron microscope (HRTEM) and energy dispersive X-ray (EDX) spectroscopic study. The blue shift of surface plasmon resonance (SPR) band with increasing mole fraction of silver has been interpreted due to dampening of core, i.e. Au SPR by Ag. The dependence of nonlinear optical response of spherical core @ shell nanoparticles has been investigated as a function of relative composition of each metal. Simulation of SPR extinction spectra based on quasi-static theory is done. A comparison of our experimental and the simulated extinction spectra using quasi-static theory of nanoshell suggests that our synthesized bimetallic particles have core @ shell structure rather than bimetallic alloy particles. [ABSTRACT FROM AUTHOR]

Abstract: Here, we report synthesis of star shape gold nanoparticles using seed mediated growth process. Ag+ ions have been used to catalyze the anisotropic growth of gold particles in the growth solution. Star like gold nanoparticles are characterized using UV–vis and TEM study. Excitation of localized surface plasmon of star shaped gold nanoparticles by the visible radiation results broad and intense localized surface plasmon resonance excitation band. Emission spectra of nanostars upon excitation at 230nm and 480nm has been explained due to localized plasmon at the edge of star like particle and the longitudinal mode of these anisotropically grown gold nanoparticles. [ABSTRACT FROM AUTHOR]

Abstract: Methyl cellulose (MC) capped gold nanoparticles are successfully prepared through a simple route. Synthesis is based on the reduction of aqueous HAuCl4.4H2O by hydrogen gas at 85°C and methyl cellulose has been used as encapsulating agent. Gold nanoparticle so-prepared are characterized by UV–Vis, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and high resolution transmission electron microscopy (HR-TEM). Methyl cellulose encapsulated gold hydrosol shows broad surface plasmon resonance (SPR) band with maxima at 537nm along with a broad tail at 635nm. In accordance with the SPR band, HRTEM micrograph shows two broad distributions of particles, most of them are small and spherical and nearly 25% particles are bigger with uneven shapes. [Copyright &y& Elsevier]