The optical properties of gold nanoparticles have been known for a number of years and recent advances in laser power have now allowed the non-linear optical properties to be studied. In this short review paper, the various theories that have been used to describe the optical properties of gold nanoparticles are presented. Methods of preparing gold nanoparticles in glasses are explained briefly, as well as characterization techniques. The optical properties of gold nanoparticles are reviewed, as well as the effects of particle size, shape, concentration and glass type.

The optical properties of gold nanoparticles have been known for a number of years and recent advances in laser power have now allowed the non-linear optical properties to be studied. In this short review paper, the various theories that have been used to describe the optical properties of gold nanoparticles are presented. Methods of preparing gold nanoparticles in glasses are explained briefly, as well as characterization techniques. The optical properties of gold nanoparticles are reviewed, as well as the effects of particle size, shape, concentration and c. Effects Of Nanoparticle SizeThe relationship between optical properties and nanoparticle radius has been studied in glasses with dispersed colloid Au nanoparticles (111,112). The peak plasmon wavelength shifts continuously to longer wavelengths with increasing average particle radius. A similar dependence was seen in silica glasses dispersed with Au colloid particles (112,113). Foss et al. (68) found significant transparency in the near-IR region and strong extinction in the visible for particles with nearsphere like shape. The wavelength of maximum extinction increased with increasing particle radius, giving rise to colour variations (red-purple for 30 nm size and blue-green for 60 nm size). This is shown in Figure 1. This was consistent with the findings of Mie (17). Hosoya et al. (73) and Muto et al. (102) found in Au:Al2O3 thin films that the spectra broadened and the peak shifted to longer wavelengths as the particle size decreased. Muto et al. (102) explained it as due to charge transfer from the metal particles to the amorphous oxide by the aluminium-metal bonds used in adhesion. The decreased electron density of the metal particles gives rise to the blue-shift. This behaviour was opposite to that of Au:SiO2, and indicates that the matrix has an effect on the blue-or red-shift of the plasmon peak with size.As the wavelength of the surface plasmon resonance changes with particle size, the χ (3) is also expected to change with size. Fukumi et al. (60), found χ (3) to be approximately proportional to the fourth power of the particle radius. They also found that χm (3) (of the metal particles on their own) had negligible dependence on the particle radius. The value of χm (3) = 2.5 x 10 -8 esu agreed with that of Hache et al. (32) and Bloemer et al. (114). Hornyak et al. (69) prepared Au nanoparticles in nanoporous alumina membranes, and absorption properties for nanoparticles of size 52 nm down to 16 nm, and with various aspect ratios. They used a modified form of MG theory, called the dynamic MG (DMG) theory (68), to model the optical properties. They found that as the nanoparticle size decreased, the wavelength of the maximum absorption intensity max approached the value predicted by DMG theory. For the smallest diameter particles, (16 nm), the values were identical with DMG theory, and they suggested that there was a quasi-static DMG limit ( max does not change from ~5 08 nm) for nanoparticles of diameter 16 nm. Alvarez et al. (115) pr...