Linear and nonlinear optical properties of sol-gel-derived Au nanometer-particle-doped alumina

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Abstract
The precursor Au-doped alumina gel film was prepared by a sol-gel method using HAuCl4⋅4H2O and alumina sol derived from AlCl3⋅6H2O. The precursor gel was heat treated in a H2 gas flow at 300–800 °C. Average particle diameters of the Au particle of doped films were in the range of 4.6–12.7 nm. In the absorption spectra of the film, plasmon resonance absorption was strongly dependent on the heat treatment temperature of the alumina matrix, showing more sharp spectra and significant red shift with decreasing particle size. It was interpreted by a modified Mie–Drude equation by taking into consideration of a spilling out of electrons from the Au particle to the alumina matrix. The measured values of χm(3) of the doped films are in the range of 9.2×10−6–4.0×10−5 esu in the neighborhood of plasmon resonance wavelength of 530–570 nm. These are larger than those reported for the other doped systems. A dominant nonlinear response on the 1–3 ps time scale was obtained, reflecting higher thermoconductivity of alumina compared to that of conventional matrix such as SiO2.