Silica Colloidal Crystals with Ethanol Solvent

We have prepared a silica colloidal crystal with ethanol, which has a face-centered cubic structure and a corresponding photonic band gap located in the visible region, determined by Kossel ring analysis and the transmission spectra. A special feature is an apparent variation of its lattice constant, as well as the gap frequency, with sample height. The Raman scattering induced by a picosecond laser at different heights of the colloidal crystal has been measured. It is found that the intensity of the Raman scattering is not related sensitively to the photonic gap, even though the Raman-Stokes Wavelength is inside the gap.