Fabrication and optical assessment of sol-gel-derived photonic bandgap dielectric structures

We present the details of the Sol-gel processing used to synthesize silica spheres, with particular attention to the conditions that permit to tailor their dimension. We have elaborated a protocol in order to obtain silica micro spheres with low polydispersivity and we have demonstrated that large well-ordered crystals of synthetic opal, that exhibit a photonic stopband, can be produced in few days by vertical deposition and evaporation-assisted sedimentation deposition methods. Scanning electron microscope was employed to characterize the samples reflectance and transmission measurements were used to put in evidence the high quality of the realized opals. Starting from the silica spheres, core-shell-like Er3+-activated silica spheres were also prepared, where the core is the silica sphere and the shell is an Er 2O3SiO2 coating. Morphologic, structural and spectroscopic properties were investigated by scanning electron microscope and luminescence spectroscopy. The emission of 4I13/2 -> 4I15/2 of Er3+ ion transition with a 27 nm bandwidth was observed upon excitation at 514.5 nm. The 4I 13/2 level decay curves presented a single-exponential profile, with a lifetime of 12.8 ms.