Observation of discrete localized surface plasmon (LSP) states in isolated nanoscaled Ag-particles synthesized via photochemical reduction route

Nanoscience Laboratory, Department of Physics, Tezpur University, P.O. Napaam, 784028 Assam, India

Corresponding author: best@tezu.ernet.in

Received: 8 July 2008
Revised: 8 December 2008
Accepted: 12 February 2009
Published online: 15 April 2009

Abstract

Metallic Ag-nanoparticles have been synthesized by catalyst free chemical and photochemical reduction processes. During photochemical synthesis, the samples were illuminated independently by unpolarized and radially-polarized continuous laser beams (λ = 632.8 nm). The nanoparticles were characterized by bright-field transmission electron microscopy (TEM), linear absorption spectroscopy and fluorescence excitation/emission spectroscopy. Compared to other growth-conditions, sample prepared under radially polarized beam essentially displays well-separated, spherical nanoparticles with a narrow size distribution around average size of 6 nm. In addition, an outstanding enhancement in the fluorescence as large as 39% has been achieved along with observation of distinct localized surface plasmon states. Though the sample produced under unpolarized light could exhibit discrete plasmon states, better resolved states were observed in case of use of radially-polarized beam. It is expected that the radially polarized light could induce resonance energy transfer and hence could control growth conditions giving rise to absolutely unclustered Ag-nanoparticles. Detecting such localized surface plasmon states and understanding conditions of high quantum yield would be promising for single molecule fluorescence, superresolution microscopy and other nanoscopic applications.