Synthetic opals based on silica-coated gold nanoparticles

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 of each other and their relative influence can be separated through infiltration with liquids of varying refractive index.