Tuning of ordered porous skeleton structures

Inverse opals with skeleton structure are photonic crystals with two complete band gaps. Additionally to the gap between eighth and ninth bands typical for inverse opals, they can have a gap between fifth and sixth bands if the refractive index exceeds 2.9. The currently known skeleton structures are formed by a sol–gel process. This process delivers different structural parameters depending on the synthesis details. A connection among the structural parameters is revealed and interpreted in this paper. The structures consist of very porous titania cylinders which are not sufficient to obtain a full band gap. They offer, however, a possibility of improvement by filling or coating of the porous cylinders with high-refractive index materials. The optimum coating thickness is determined theoretically.