Self-assembled 3D photonic crystals from ZnO colloidal spheres

We present a novel method for the controlled synthesis of monodisperse ZnO colloidal spheres. These spheres are self-assembled into fcc periodic arrays. Optical measurements, including reflection-mode optical microscopy and transmission and single-domain reflection spectroscopy, reveal that the periodic arrays exhibit a photonic band gap in the (1 1 1) direction of the fcc lattice, and calculations are presented to estimate the effective value of the refractive index of the colloidal spheres. Finally, photoluminescence (PL) measurements show that the ZnO lasing thresholds are lower in periodic structures than in random arrays of identical spheres.