Synthesis and optical properties of opal and inverse opal photonic crystals

We describe the synthesis of two complementary photonic crystals: opal and an inverted opal structure consisting of air spheres in a titania matrix. From optical measurements and comparison with the literature, the mechanical strength and effective refractive index are increased by sintering for opal and because of compression for the inverse opal. However, this is at the expense of reducing the PBG in the [1 1 1] direction.