Refractive index controlled plasmon tuning of Au nanoparticles in SiO2-ZrO2 film matrices.

Au-plasmon tuning has been accomplished by controlling the refractive index (n) of the embedding film matrix. The refractive index of the film matrices were controlled by changing the molar ratios of low (SiO2) and high index (ZrO2) components following sol-gel reactions. Thus, Au nanoparticles doped films were prepared from SiO2-ZrO2 inorganic-organic hybrid sols of variable molar ratios containing HAuCl4 following the dip-coating method. The film samples deposited on glass substrates were obtained after drying, UV-treatment, and subsequent heat-treatment at 500 degrees C in air. The nominal mol ratios of SiO2:ZrO2 were 1:0, 1:1, 1:2.3, and 1:4. 3 equivalent mol% Au-97% total oxide (SiO2 + ZrO2) was maintained in the final heat-treated films. FTIR studies confirmed good homogeneity of Si-Zr network in the Zr-containing films. The UV-treatment has been introduced to facilitate the decomposition of HAuCl4 in the hybrid matrix prior to the heat-treatment step. The main Au-plasmon peak, in the case of a SiO2 host (SiO2:ZrO2 = 1:0, n = 1.410), observed at about 546 nm, gradually red-shifted to 592 nm upon increasing the ZrO2 content (SiO2:ZrO2 = 1:4, n = 1.847). Transmission electron microscopy of the final heat-treated (500 degrees C) films showed existence of plate-like (triangular and hexagonal) Au nanoparticles (25-50 nm) along with relatively smaller nanoparticles of about 10 nm in size. X-ray diffraction patterns reveal that the Au nanoparticles have a (111) orientation.

Nonlinear optical absorption and switching properties of gold nanoparticle doped SiO2-TiO2 sol-gel films.

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.