Abstract
A novel process consisting of a synthesis of gold hydrosol using tetrakis (hydroxymethyl) phosphonium chloride (THPC) reduction and a sol–gel process using tetramethylorthosilicate (TMOS) for the encapsulation of gold nanoparticles (Au/SiO 2: 0.1–1 wt% Au) in a matrix of silica gel without the aid of any external stabilizing agent or organically modified sol–gel monomers is described. The optical absorption spectra showed the typical surface plasmon resonance for Au at around 530 nm, corroborated by X-ray photoelectron spectroscopy. Transmission electron microscopy revealed the existence of spherical Au particles in the matrix. The mean diameter of Au nanoparticles in gels varied from 10 to 20 nm, supported by X-ray diffraction data. The third-order optical non-linearity ( χ 3) determined by the degenerate four-wave mixing (DFWM) method exhibited a value of 4.6 × 10 −11 esu for a gel with 0.1 wt% Au.
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