Varying the Optical Stop Band of a Three-Dimensional Photonic Crystal by Refractive Index Control

A method was developed to continuously adjust the position of the stop band of inverse opal by controlling the refractive index. The inverse opal films were fabricated using a coassembly of monodispersed polystyrene spheres and nanoparticles of silica and titania from aqueous suspensions followed by a calcination treatment. Varying the ratio of silica and titania in the suspensions gave the ability to finely adjust the refractive indices, which as a result changed the stop band.