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 art ificial opals where uniform silica globules are closely packed in a face-ce ntered cubic lattice. Sintering of the samples increases their rigidity wit hout affecting the 3D regular structure. Artificial opals exhibit a photoni c bandgap-an orientation dependent forbidden frequency gap in the visible s pectral range. The photonic bandgap feature makes artificial opals promisin g candidates for optical applications. (C) 1999 Elsevier Science S.A. All r ights reserved.