Process optimization of sol-gel derived colloidal photonic crystals

Three-dimensional photonic bandgap structures have been synthesized by a colloidal/sol-gel route, starting with the self-organization of polystyrene microspheres into opals by dip-coating, sedimentation or vertical convective self-assembly, followed by sol-gel infiltration of the interstices with silica, titania or a silica-titania mixture, by dip-coating and removal of the polymeric template. The structural and optical properties of the opals and inverse opals prepared by this method have been studied by scanning electron microscopy and visible infra-red spectroscopies to assess the relationship between their structure and the photonic properties obtained. The optical transmission and reflection spectra of the opal and inverse opal structures have also been simulated by the Translight Software code, using the Transfer Matrix method, for different numbers of stacked layers, showing reasonable agreement with the experimental results. By optimizing the fabrication parameters, colloidal photonic crystals of good quality have been obtained, with reduced defect concentrations and increased mechanical strength.