Optical studies of porous glass media containing silver particles

We prepared Ag-glass composites by impregnating porous glass with a AgNO₃ solution. The samples were then reduced (in a hydrogen atmosphere) and densified before they were characterized by x-ray diffraction and electron microscopy. The growth of the metal particles inside the glass was studied by a transmission electron microscope. The optical properties of these compos- ites were studied by measuring the reflectance between 10 000 and 40 000 cm^-1. To explain the measured reflection spectra, we used two different theoretical approaches, i.e., the Maxwell-Garnett theory (MGT) and a lattice gas model developed by Persson and Liebsch (PLT). This latter model was more successful in accounting for the red shift, the line broadening, and the reduction of the peak in the reflectance spectra than the MGT. However, our measured spectrum still cannot be explained quantitatively by the PLT. In particular, there is a ``dip'' in the reflection spectra whose position depends on the mean size of the Ag particles. This cannot be explained by either theory.