A suspension of particles is rapidly self-assembled with a minimal number of defects into a three-dimensional array of particles onto a substrate under simultaneous sedimentating and annealing forces. This array of particles may be ordered as an opal structure. Optionally, the synthesized structure may incorporate an electrolyte into the suspension and be used as a sacrificial form for micromoulding an inverse structure. The inverse structure may exhibit a photonic band gap. Optionally, necking and material composition may be adjusted after micromoulding. These structures are useful to a wide variety of applications. The photonic band gap structure may be heated to function as a light source. The light source may be fitted into standard sockets.