Tunable optical properties of metal nanoparticle sol-gel composites

We demonstrate that the linear and non-linear optical properties of sol-gel s containing metal nanoparticles are highly tunable with porosity. Moreover , we extend the technique of immersion spectroscopy to inhomogeneous hosts, such as aerogels, and determine rigorous bounds for the average fractional composition of each component, i.e., the porosity of the aerogel, or equiv alently, for these: materials, the catalytic dispersion. Sol-gels containin g noble metal nanoparticles were fabricated and a significant blue-shift in the surface plasmon resonance (SPR) was observed upon formation of an aero gel, as a result of the decrease in the dielectric constant of the matrix u pon supercritical extraction of the solvent. However, as a result of chemic al interface damping and aggregation this blue-shift does not strictly obey standard effective medium theories. Mitigation of these complications is a chieved by avoiding the use of alcohol rind by annealing the samples in a r educing atmosphere. (C) 2001 Elsevier Science B.V. All rights reserved.