Ultraviolet absorption of Au nanoparticles, embedded in dielectric matrices: A theoretical study using a simple model

Abstract

The optical absorption (OA) spectra of spherical Gold (Au) nanoparticles (NPs) have been studied theoretically using a simple model based on the effective medium theory. In this study we have calculated the OA of Au NPs of different radius embedded in silica glass. In this calculation we have varied the radius of the particle from 1 nm to 50 nm in the wavelength range 200 nm −800 nm. The OA spectra so calculated exhibit two strong absorption bands: one at ∼245 nm (UV-regime) and another at∼531 nm (visible region). The absorption band corresponding to visible region is due to the well-known surface plasmon resonance (SPR) while the band in the UV regime appears due to the inner band transition generally from inner d-band to the conduction band above the Fermi level. A blue-shift of both the bands with decrease in NP radius (below 10 nm) has been observed. Here the intensity of the interband absorption in the UV region is smaller than the corresponding SPR band. To confirm and understand clearly the origin of the UV band, a systematic variation of the dielectric constants (DC’s) of the embedding medium has been carried out. The UV band shows no any peak shift with the variation of DC values. Although, SPR peak changes its position with DC values of the surrounding medium. As there is no effect of the DC values on the peak position of the UV band, one would expect that this band arises from the inner band transitions known as interband transition (IB).