Optical properties of small metallic particles in a continuous dielectric medium

Abstract

The dielectric function of an inhomogeneous system consisting of small particles in a dielectric host material is investigated using a lattice gas model to describe the topological disorder among the particles. By applying the coherent potential approximation, an effective single-particle polarisability is found, which contains the influence of the local electric fields arising from randomly distributed particles. In the Maxwell-Garnett theory it is assumed that these fields in a random distribution of dipoles are the same as those calculated for a cubic array of dipoles. The disorder is shown to give a substantial red shift of absorption peaks and a comparable blue shift of loss lines. Moreover, absorption as well as loss features are very strongly broadened. These kinds of shifts and enhanced linewidths have been observed experimentally for many systems. A detailed comparison with measured spectra is given for silver particles immersed in a gelatin matrix.