Optical properties of graded colloidal nanocrystallines with tunable structure

We propose a class of graded colloidal crystalline materials which consist of polydisperse metallodielectric nanoshells stacked in layers. We take the Lekner-Lishchuk summation method to treat the graded systems which are not tractable by conventional approach such as Ewald-Kornfeld methods. It is demonstrated that this kind of graded materials exhibit a series of sharp peaks, which merge in a broadened resonant absorption band in the optical region, in contrast to colloidal crystal containing monodisperse nanoshells or nanoparticles. Effects of various gradient profiles of the ratio of the inner/outer radii in the nanoshells and lattice geometries on the optical properties are discussed. These materials are not hard to fabricate by contemporary nanofabrication techniques and they shall be useful in the engineering of optical nanomaterials.