A method for making aerogel doped with gold nanoparticles (GNPs) produces a composite material with a well-defined localized surface plasmon resonance peak at 520 nm. The width of the extinction feature indicates the GNPs are well dispersed in the aerogel, making it suited to optical study. A simple effective medium approximation cannot explain the peak extinction wavelengths. The plasmonic field extends on a scale where aerogel cannot be considered isotropic, so a new model is required: a 5nm glass coating on the GNPs models the extinction spectrum of the composite material, with air (aerogel), methanol (alcogel), or toluene filling the pores.
Grogan, M. D. W., Heck, S. C., Hood, K. M., Maier, S. A., & Birks, T. A. (2011). Structure of plasmonic aerogel and the breakdown of the effective medium approximation. Optics Letters, 36(3), 358-360. https://doi.org/10.1364/OL.36.000358