The size influence of silica microspheres on photonic band gap of photonic crystals

The size influence of silica microspheres on the photonic band gap (PBG) of three-dimensional face-centered-cubic (fcc) photonic crystals (PCs) is studied by means of colloidal photonic crystals, which are self-assembled by the vertical deposition technique. Monodispersed SiO2 microspheres with a diameter of 220 320 nm are synthesized using tetraethylorthosilicate (TEOS) as a precursor material. We find that the PBG of the PCs shifts from 450 run to 680 nm with silica spheres increasing from 220 to 320 run. In addition, the PBG moves to higher photon energy when the samples are annealed in a temperature range of 200-700 degrees C. The large shift results from the decrease in refraction index of silica due to moisture evaporation.