Transmittance spectra in different media (air, water and water-glycerol mixtures) for sintered opals made of Au@SiO2 particles with 15 nm core diameter and 225 nm total diameter. The corresponding refractive indices are indicated. Two dips can be observed: one is due to Bragg diffraction at normal incidence, the other is a plasmon resonance. As crystal refractive index is matched by the infiltrating liquid, Bragg diffraction and dissuse scattering effects turn weaker.

ABSTRACT

High-quality solid colloidal crystalline assemblies have been prepared through the sedimentation of monodisperse silica spheres, each containing a single gold nanoparticle in its center. The metal centers provide a strong absorption at a well-defined wavelength that complements the Bragg reflection arising from the periodic structure of the opal. The optical properties of these systems were characterized through transmission and specular reflectance measurements. It is clearly shown that absorption and diffraction are basically independent from each other and their relative influence can be separated through infiltration with liquids of varying refractive index.