Surface plasmon resonance broadening of metallic particles in the quasi-static approximation: a numerical study of size confinement and interparticle interaction effects

The width of the surface plasmon resonance of metallic particles increases as the particle size reduces due to confinement effects that modify the metal dielectric function. In the limit of very low particle concentration, particle size can be directly related to the plasmon width. However, as concentration increases, the interaction among particles induces additional broadening. Numerical computation of the effective dielectric function of systems consisting of monodisperse and randomly distributed particles embedded in a dielectric matrix enable us to quantify the influence of both size and interaction effects. It is shown that for noble metals the contribution of interparticle interaction to plasmon resonance width cannot be neglected even at volume concentrations of a few per cent. The results presented here can be useful in extending nanoparticle sizing from optical extinction spectroscopy beyond the dilute limit required by classical Mie theory.