Investigation On The Preparation And Photoluminescence Properties Of Ag-SiO₂ Composite Film

Ag-inorganic nano-composite systems possess interesting properties of nonlinear optical susceptibility, optical absorbance and photoluminescence. These fine properties are mainly due to the surface plasmon resonance and inner electron transition of silver nanoparticles. When the size, shape and distribution of silver particles changed, the intensity and position of the surface plasmon resonance and the split extent of electron step can be modulated, and thus we can get opto-functional materials to meet different demands.In this paper, stable sols can be prepared by using TEOS and AgNO₃ as the main predecessors and CH₃OCH₂CH₂OH as the solvent. Then the Ag-SiO₂ composite films, with different doping concentration of Ag(Ag/Si), can be successfully prepared by dip-coating method.The experiment results show that the composite films have different optical properties when it is prepared on different substrates. As on the undersurface of the floating glass, the bivalent stannum ions can deoxidize univalent silver ions, then Ag-SiO₂ composite films with silver nanoparticles distributed can be obtained. The composite film presented the surface plasmon resonance absorption peak of Ag nanopartides around 400nm, the surface enhanced Raman Scattering and better properties of photoluminescence. While films prepared on glass slide and the upper-surface of the floating glass exhibit no characteristic peak, no phenomena of surface enhanced Raman signals and relatively low luminescence intensity. The results also demonstrated that the process of heat treatment does play an important role on the optical properties of the composite films, as it can influence the nucleation and growth of the particles. Besides, when all of the above process parameters are optimized in our experiment conditions, doping of lanthanum ions (La³+) and aluminum ions (Al³+) respectively into the composite can have interesting effect on the films properties. The rare-earth ion of La³+ is low-cost and no fluorescent material. It can help to transfer energy to the main body during the excitation process. While the common metal ions of Al³+ can influence the surroundings around the main bodyof silver. These two ions will both infect the photoluminescence properties of the composite films. And simultaneously, the doping ions, to a certain extent, can restrain the surface plasmon resonance absorption and minish the size of Ag nanoparticles.Properties of Ag-SiC>2 composite films mainly depend on the chemistry state of silver, the size of silver particles and its distribution in the films. The surroundings around Ag* is also an important factor that should not be neglected. Silver in the system always exist in multi-forms. The quantity of a certain state may alter as the condition of preparation changed. Then the absorption and luminescence spectrum may exhibit different characteristics. As a result, it can be an effective way to gain good optical properties of the Ag-SiO2 composite films by controlling and optimizing the process parameters.