Stop band tuning of three-dimensional photonic crystals through coating of semiconductor materials

Fine-tuning of stop band positioning, ranging from several nano meters to several tens of nano meters, was achieved through sequential thin layer coating of semiconductor materials onto the constituent particles of a three dimensional silica-based photonic crystal. Several semiconductor materials, including TiO₂, CdS, and ZnSe, were successfully used to achieve a controllable red-shift of the stop band position of synthetic opal. The stop band shift observed in the present work can be explained by Bragg's law. The coating operation is equivalent to replacing the lower dielectric constant of the material, i.e. the air around it, with a higher dielectric constant semiconductor materials, thus increasing the effective refractive index of the structure and giving a red-shift in the stop band.