Papers by Author: Ilaria Cacciari

Abstract: We report on fabrication and characterization of two different opal-like structures: (i) crystal exhibiting mechanochromism, i.e. change of colour when subjected to mechanical stress, composed of closely packed colloidal polystyrene particles (CPCP) embedded in a poly-dimethylsiloxane (PDMS) elastomeric matrix; (ii) metallo-dielectric systems (MDCS), based on the realization of inverse silica opal and following attachment of gold nanoparticles on the silica network of the inverse colloidal structure. Optical measurements, performed on the two structures, have demonstrated that: (i) when an horizontal strain is applied on the CPCP embedded in PDMS, a blue shift of the diffraction peak occurs as a function of the applied strain and (ii) MDCS have unique optical properties that combine the localized surface plasmon resonance (LSPR) of gold nanoparticles (Au NPs) with the photonic band gap features of colloidal crystal structures. Finally, preliminary results on MDCS used as SERS substrate evidence a higher increase of the Raman signal in respect to that observed for others metallic structures.

Abstract: We present the details of the sol-gel processing used to realize inverse silica opal, where the silica was activated with 0.3 mol% of Er3+ ions. The template (direct opal) was obtained assembling polystyrene spheres of the dimensions of 260 nm by means of a vertical deposition technique. The Er3+-activated silica inverse opal was obtained infiltrating, into the void of the template, the silica sol doped with Er3+ ions and subsequently removing the polystyrene spheres by means of calcinations. Scanning electron microscope showed that the inverse opals possess an fcc structure with a air hollow of about 210 nm. A photonic band gap in the visible range was observed from reflectance measurements. Spectroscopic properties of Er3+activated silica inverse opal were investigated by photoluminescence spectroscopy. A bandwidth of 21 nm was measured for the 4I13/2 → 4I15/2 transition of Er3+ ions upon excitation at 514.5 nm. The luminescence decay curve of the 4I13/2 metastable state of the Er3+ ions presents a lifetime τ = 16.8 ± 0.1 ms giving a very high quantum efficiency of the fabricated system. Core-shell Er3+-activated silica spheres, where the core is the silica sphere and the shell is an Er2O3-SiO2 coating is proposed as a possible route for opal fabrication. For core-shell system a quantum efficiency of about 70% was estimated.