Tailoring localized surface plasmons in Ag–Al alloys’ nanoparticles

Abstract

Optical absorption properties of Ag–Al alloys’ nanoparticle (NPs) of radius of 10 nm embedded in silica for Al or Ag molar concentration in the range of 0.0–0.25 have been studied theoretically using a simple model. In case of monometal (Ag and Al) NPs, one localized surface plasmon resonance (LSPR) band, for each, (at ∼402 nm for Ag and ∼217 nm for Al) has been observed as expected from the corresponding real parts of dielectric constants. For alloys, the LSPR peak positions have been found to appear at wavelength positions in between the LSPR peaks corresponding to Ag and Al NPs confirming the Ag–Al alloys formation. The formation of these alloys in nano-phase was possible because of nearly same lattice parameters of Ag and Al. A blueshift (up to ∼54 nm, from visible to UV regions) of the LSPR peak for Ag1-xAlx alloy and a redshift (up to ∼20 nm, from deep–UV to UV regions) of the LSPR peak for Al1-xAgx alloy have been seen with increase in Al and Ag concentration, respectively. Additionally, for both the alloys the width of SPR bands have been found to increase linearly with increase in Al or Ag concentration due to electron dissipation caused mainly by electron scattering on impurity-induced defects with increase in impurity concentration in alloy NPs. Appearance of a broad LSPR (gap resonance) band is observed in addition with the usual LSPR for Ag1-xAlx due to the grain boundaries within the alloy NPs.