In situ generation of Au nanoparticles in UV-curable refractive index controlled SiO2-TiO2-PEO hybrid films

UV-curable inorganic (SiO2-TiO2)-organic (polyetheylene oxide [PEO]) hybrid films with high refractive index (RI) values were synthesized, and Au nanoparticles were generated in situ inside such hybrid films. The hybrid films and the corresponding Au-doped films were prepared from sols derived from a mixture of silicon, titanium, and organically modified silicon alkoxides and gold chloride following a sol-gel dip-coating method. An equivalent SiO2/TiO2/PEO/Au molar ratio (nominal) of 27.7:46.1:23.0:3.2 was maintained in the sol. UV treatments of the dried (90 degrees C) films with energies from 5.3 +/- 0.1 to 53.0 +/- 0.5 J cm(-2) resulted in densification with a gradual increase of the RI value up to 1.75. Drying and UV treatments of the corresponding HAuCl4-incorporated hybrid films induced generation of An nanoparticles and showed the characteristic Au-plasmon peak. A gradual red-shifting of the Au-plasmon band from 545 to 571 nm was observed with respect to the UV-treatment energies. This red-shifting is initially due to the increase of RI of the film, and in the later stages it is mainly due to the Au-plasmon coupling concurrently with the slight increase of RI values. Transmision electron microscopy of the UV-treated films showed the presence of densely populated Au nanoparticles of mainly 4-5 nm in size inside the hybrid SiO2-TiO2-PEO film matrix.