| Ag-inorganic nano-composite systems have attracted special attention during the past decade, due to their interesting properties such as high third-order nonlinear optical susceptibility, photoluminescence and photochromism, etc. In this paper, Ag-SiO2 nano-composite films on commercial float glasses have been prepared by sol-gel method. The optical absorption (OA) and photoluminescence (PL) properties of the films have been studied. The microstructure of the films with Ag/Si=0.10 (atom ratio), and the formation of the silver nanoparticles during theheat-treatment, have been analyzed.The Ag-SiO2 composite sols, with Ag/Si=0.01-0.10 and stable Ag+ availability, have been prepared after optimizing the technical parameters, by using TEOS and AgNO3 as the main predecessors and functional silane (APS) as the completion of Ag+. The composite films on float glasses have been prepared, by using dip-coating method with drawing speed 8-32cm/min. The gelification process of the composite has been investigated by using DSC-TG and SEM measurements. The results show that the organic residual has been decomposed completely and the crack-free films can be obtained after heat-treated higher 450℃.Based on Mie and Maxwell-Grarnett (M-G) effective medium theory, the effects of technical factors on the optical absorption properties of the samples have been analyzed. The heat-treatment temperature, the doping concentration of Ag (Ag/Si) and drawing speed of the substrates can regulate the size, amount and distribution of silver nanaparticles in the matrix, and then influence the optical absorption of the samples.The PL spectra of the Ag-SiO2 composite films have been obtained from the fluorophotometer. There are three excitation centers in the samples located at 228nm, 266nm and 325nm. The photoluminescence properties and mechanisms of samples, " excited with 228nm and 325nm, have been studied. The results indicate that the photoluminescence mostly associate with Ag, which are in different chemical states. Excited with 228nm, the emission bands centered at about 365nm and 460nm originate from the electron transitions of 1D2-1S0 and 3D-1S0 in Ag+ respectively, and the emission band at 400nm results from the surface plasma resonance of the silver nanoparticles, which aggregated near the surface of the films. Excited with 325nm, theemissions bands of 350~500nm and 640-690nm due to the silver clusters and silver nanoparticles respectively.The microstructure of the films has been investigated by XRD, FT1T, XPS and TEM. The results indicate that the SiO2 matrix exists in form of noncrystalline state, and the silver nanoparticles distribute in the matrix homogenously. The entrance of Na+, which comes from the substrates, can change the structure of Si-O network of the film during the heat-treatment.The combination of OA and PL spectra can be used as a tool to distinguish silver nanoparticles, silver clusters, silver atoms and silver ions in the sol-gel films, and can reflect the coupling of Ag and matrix in some degree. This analytical method has been put into practice to analyze the formation of silver nanoparticles during the heat-treatment. The results show that the chemical composition of substrate surface and the heat-treatment regime are the major influencing factors on the formation of silver nanoparticles. During the heat-treatment, Sn2+ in the bottom face of the float glasses reduce Ag+ to Ag? which is the key to form silver nanoparticles. And the interdiffusion between Na+ and Ag+ promotes the formation of silver nanoparticles.
|
PDF Full Text Request