Diversity of materials and functionalities in composite opals

The ability to combine different materials in the framework provided by opals generates a wealth of functionalities. Different synthetic routes are required and strategies are designed to allow the combination of organic and inorganic matrices and infill with metals, semiconductors, insulators. The use of such tools helps deepen the understanding of the interactions of light and photonic crystals. Bare opals are a very appropriate playground for testing and studying various photonic band gap properties like light coupling to block states for instance. This casts a good deal of light on experiments of transmission and reflectance and their relationship with the photonic bands. Phase measurements can be obtained from white light interferometry experiments. A careful infiltration allows a controlled tailoring of the PBG properties of the composite. The infiltration with ZnO can be taken as a typical example of band gap engineering. Si is synthesized by templating on polystyrene opals that were previously treated with CVD grown SiO₂. This allows us to raise the temperature to the levels needed for Si synthesis and opens the door to new materials, composites and topologies.