Sol–gel photonic bandgap materials and structures

Abstract

In this work, one-dimensional multilayer structures of periodically alternating low refractive index (SiO2) and high index (TiO2) materials have been deposited by sol–gel spin-coating, in the form of dielectric mirrors (distributed Bragg reflectors) and Fabry-Perot microcavities. Some of the microcavities were doped with europium. These structures have been characterized structurally (by X-ray diffraction, Raman spectroscopy and field emission-scanning electron microscopy) and optically (by ellipsometry and visible–near IR spectroscopy); their optical properties, namely the stop band of high reflectivity and, in the case of the microcavities, the cavity mode and the photoluminescence behavior of the Eu3+ ions inserted in the cavity layer, were assessed. In addition, three-dimensional-like structures have also been synthesized by a colloidal/sol–gel route, starting with the self-organization of a colloidal dispersion of polystyrene microspheres, by dip-coating or convective self-assembly, followed by infiltration of the interstices with titania and removal of the polymeric template. The structural and optical properties of the inverse opals prepared by this method have also been studied, by scanning electron microscopy and by visible reflection spectroscopy, in order to assess their photonic bandgap properties.