Visible and near-infrared silica colloidal crystals and photonic gaps

The transmission spectra at the high-symmetry points of the first Brillouin zone are measured for three face-centered-cubic colloidal crystals made of silica spheres of different submicrometer sizes. It is found that at the U point the transmission dip exists not only for an s wave, but also for ap wave. Moreover, at the W point the transmission dips of both s and p waves appear at the same wavelength. Our calculations confirm that these dips correspond to the lowest band gaps of the high-symmetry points. The structures and parameters of these crystals are determined by the Kossel-rings analysis as well as by the transmission spectra. [S0163-1829(98)01926-2].