Effect of Nanostructures on Corona Poling Assisted Second Harmonic Generation in Hybrid Organic-Inorganic Films

Abstract

Hybrid organic-inorganic films are attractive materials for an alternative manufacture of photonic devices based on non-linear second-order optical processes. However, their efficiency and stability, closely related to their chromophores non-centrosymmetric orientation, still need some improvements. The use of nanostructures in this kind of materials gives place to a change in the chromophores surrounding medium; it can be used to improve the efficiency and the stability of the chromophores orientation in the films. In this work we show that some nanostructures are able to improve significantly the organic-inorganic SiO2 films second-order non-linear optical responses. Two kinds of nanostructures were studied: some nanostructures were just immersed, but the other ones were spontaneously induced in the films. The immersed nanostructures were multi-walled carbon nanotubes and the spontaneously induced nanostructures were formed in the films by means of surfactants self-assembly. The films were synthesized by the sol-gel method and all of the films were doped with Disperse Red 1 (DR1) dipolar chromophores. The induced nanostructures were lamellar and hexagonal long-range ordered nanostructures, detected by X-ray diffraction (XRD). The second-order non-linear optical properties of the films were studied in resonance through Corona poling assisted second harmonic generation. The results show significant improvements, for some kinds of nanostructures, in the non-linear optical responses of the films. In particular, those films containing Triton X-100 showed, at a poling temperature of 120°C, an improved second-order non-linear coefficient d33 with respect to equivalent non-nanostructured films; the d33 value of those films, determined by the Maker fringes technique, was equal to 21.4 pm/V.