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Ag nanoparticle incorporated inorganic-organic hybrid silica films were prepared from sols derived from tetraethyl orthosilicate-3-(glycidoxypropyl)-trimethoxysilane-silver nitrate following a sol-gel dip-coating method. Hydrolysis-condensation of alkoxy groups and polymerization of epoxy groups formed MSi-O-SiM (SiO 2 ) and polyethylene oxide (PEO) networks respectively. A nominal composition of the film of 2.3 equivalent mol% Ag-74.4 mol% SiO 2 -23.3 mol% PEO was maintained. The precipitation of Ag nanoparticles was observed when the film was cured at 60-90 uC. UV treatment (5.3-31.8 J cm 22 ) causes coarsening of the Ag nanoparticles inside the hybrid SiO 2 -PEO film matrix. A single surface plasmon (SP) band due to Ag nanoparticles has been observed at 419 nm when the film was cured at 90 uC and UV treated with an energy of 5.3 J cm 22 . This SP band is gradually divided into three peaks upon increasing the UV treatment energy up to 31.8 J cm 22 . TEM study confirms the coarsening of small Ag nanoparticles of 3-4 nm in size, leading to the formation of spheroidal, elongated and fractal type small aggregates of Ag nanoparticles of size range y19-53 nm. The splitting of the Ag-SP band is found to be consistent with the shape of the Ag nanoparticles as observed by TEM.

UV-curable inorganic (SiO 2 -TiO 2 )-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 SiO 2 /TiO 2 /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 °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 HAuCl 4 -incorporated hybrid films induced generation of Au 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 SiO 2 -TiO 2 -PEO film matrix.

The nonlinear optical absorption and switching properties of sol-gel derived of Au nanoparticle doped SiO2-TiO2 sol-gel films having different Au-surface plasmon absorption positions are reported in this paper. The Au nanoparticles are embedded in SiO2 and SiO2-TiO2 mixed glassy film matrices with different refractive index values. To study the nonlinear absorption properties, lasers with three different wavelengths are used. The optical switching behavior is studied by using the pump-probe technique with 532 nm as the excitation wavelength. Ground state conduction band, surface plasmon band, and the free carrier band are taken as three level model to explain theoretically the obtained RSA and SA behaviors.

Several noble metal nanoparticles doped sol-gel derived thin coloured films have been synthesized and characterized. These are pure (Ag, Au, Cu and Pt), mixed/alloy (Ag-Cu, Au-Cu, Au-Ag and Au-Pt) nanoparticles in SiO 2 , Au in mixed SiO 2 -TiO 2 and SiO 2 -ZrO 2 , Au and Ag nanoparticles in inorganic-organic hybrid film matrices etc. This investigation leads to the development of tailor-made coloured coatings by tuning the surface plasmon resonance (SPR) band positions originating from the embedded nanometals by controlling mainly (i) refractive index of the film matrices and (ii) nanoalloy composition. In the later case a new layerby-layer (two-layer) synthetic protocol has been developed to prepare binary nanoalloy particles with controlled atomic ratios.