Opal-Type Photonic Crystals: Fabrication and Application

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.