Nonlinear optical behavior of Au@Ag core- shell nanostructures

Abstract

Core-shell structure has been getting tremendous research interest due to their tunable multifunctional properties, induced as a result of the co-occurrence of more than one nanostructured phases. Here we report detailed nonlinear optical studies of Au@Ag core-shell nanostructures under ns pulse excitation. The size and shell thickness of the core-shells were obtained from TEM images. A significant blue shift from 519 nm to 411 nm in surface plasmon maxima is observed on forming Ag (shell) layer on Au (core) nanosphere and a slight red shift (411 nm to 425 nm) was observed as the shell thickness increases from 7.5 to 22.5 nm. All the samples exhibited reverse saturable absorption behavior and the extent of optical limiting activity enhanced on increasing the shell thickness. Nonlinear refraction properties of the samples were also analyzed and all the samples were found to be exhibiting negative nonlinearity. Improved optical limiting activity on increasing shell thickness of the studied system could be attributed to enhanced local field effect and nonlinear scattering effect, which is confirmed from the finite difference time domain simulation analysis. The good nonlinear optical properties of Au@Ag core-shell structures ensure its potential for future nonlinear optical applications.