Spectral properties of opal-based photonic crystals having aSiO2matrix

We study the transmission and reflection of electromagnetic waves propagating in bare opal photonic crystals. We find that the incomplete gap at the $L$ point fully inhibits the transmission of waves propagating in the [111] direction for opal sample thicknesses that are easily obtainable. This property shows that bare opals could be good candidates for complete inhibition of transmission in the near-infrared and visible frequency range for given orientations. The dependence of the total reflectance on the angle of incidence has been calculated, and a good agreement has been found with available experimental data. We have also analyzed the modification of the transmission properties of bare opals induced by a sintering process. Our calculation predicts a linear decreasing of $L$-midgap frequency when the filling fraction decreases due to sintering, which is also in accordance with experiments.