Self-organization of uniform silica globules into the three-dimensional superlattice of artificial opals

Amorphous spherical silica particles with sizes ranging between 100 and 700 nm, depending on the synthetic conditions and post-preparative treatment, self-organize during slow sedimentation into a 3D solid superlattice of artificial opals where uniform silica globules are closely packed in a face-centered cubic lattice. Sintering of the samples increases their rigidity without affecting the 3D regular structure. Artificial opals exhibit a photonic bandgap - an orientation dependent forbidden frequency gap in the visible spectral range. The photonic bandgap feature makes artificial opals promising candidates for optical applications.