Fabrication and Optical effects in artificial opals infiltrated with gold nanoparticles

Three dimensional photonic crystals, in opal configuration, are attractive for their easy processability and capability of selfassemble in an ordered face centered cubic structure [1]. Moreover, they serve as template for inverse opals which, in fact for suitable dielectric contrasts, show a full band gap. Furthermore, infiltration with photoactive materials dramatically alters the optical properties of opals and allows interesting applications in fields such as photonics and optoelectronics. Among highly polarizable infiltrating materials, we focused our attention on gold nanoparticles, which are known to have a high and fast non linear optical (NLO) response. Moreover, their surface plasmon resonance energy depends on particle size and shape, as well as on the surrounding environment. The aim of this work was to develop a growing technique for NpAu infiltrated polystyrene (PS) opals and to study their optical properties. Direct infiltration of PS opals with NpAu water solutions is very difficult due to the low wettability of PS with water. Exploiting the self-assembling properties of colloidal photonic crystals it is possible to grow infiltrated opals directly form mixed suspensions of PS and NpAu. The optical quality of NpAu infiltrated opal films grown with our method allows to perform a detailed spectroscopic characterization