Photonic band-gap properties of opaline lattices of spherical colloids doped with various concentrations of smaller colloids

Monodispersed polystyrene beads have been organized into highly ordered, three-dimensional (3D) lattices using a self-assembly procedure recently demonstrated by our group. Such a 3D periodic structure consisting of high and low dielectric regions exhibits a pseudo-band gap (or a stop band) in the optical regime, with the position of this gap mainly determined by the size of the polymer beads. Doping of this 3D crystalline lattice with polymer beads of a smaller size was found to have a profound influence on the order (and thus the photonic band-gap properties) of the lattice. When the concentration of the dopant reached a certain level, phase segregation occurred which led to the formation of samples with relatively smaller domain sizes. In accordance, the attenuation (or rejection ratio) of the stop band also decreased monotonically as the doping level was increased.