Preparation and morphological and optical characterization of azo-polymer-basedSiO2 sonogel hybrid composites

Abstract

The well-established catalyst-free sonogel route was successfully implementedto fabricate highly pure, optically active, solid state polymeric azo-dye/SiO2-based hybrid composites. Bulk samples exhibit controllable geometrical shapes andmonolithic structure with variable dopant concentrations. Since the implemented azo-dyechromophores exhibit a push–pull structure, hybrid film samples were spin-coated onITO-covered glass substrates; molecular alignment was then performed via electrical polingin order to explore the quadratic nonlinear optical performance of this kind of composite.Comprehensive morphological, spectroscopic and optical characterization of the sampleswere performed with several experimental techniques: atomic force microscopy,x-ray diffraction and infrared, Raman, photoluminescent and ultraviolet–visiblespectroscopies. The linear refractive indices of both bulk and thin film samples weremeasured according to the Brewster angle technique and a numerical analysis of thetransmission spectral data, respectively. Regardless of the low glass transitiontemperatures of the studied polymers, some hybrid film samples were able to displaystable nonlinear optical activity such as second harmonic generation. Resultsshow that the chromophores were satisfactorily embedded into the highly pureSiO2 sonogel network without significant guest–host molecular interactions, thus preserving theiroptical properties and producing sol–gel hybrid glasses suitable for optical applications.