Preparation and second-order optical nonlinearity of inorganic–organic hybrid films

The sol–gel technique has been used to prepare a thin film for second-order nonlinear optics (NLO). An azo-dye molecule 2,5-dimethyl-4-(4′-nitrophenylazo)phenol (DMNPAP) was covalently bonded to the silicon oxide network through hydrolysis and co-condensation between the alkoxysilane dye and tetraethyl silicate (TEOS) in relatively high loading densities (43 wt%). The resulting film showed a thermal stability up to 302 °C in thermogravimetric analysis (TGA) thermograms and a flat surface morphology in atomic force microscope (AFM) image. The orientation behavior of the poled film was studied by UV–visible spectroscopy. The NLO activity (d33), which was estimated to be 6.5 pm/v at 1064 nm by in situ second harmonic generation (SHG) measurement, the thermal stability of the second-order nonlinearity was also reported.