ORIGIN OF ABSORPTION-BANDS OBSERVED IN THE SPECTRA OF SILVER ION-EXCHANGED SODA-LIME-SILICA CLASS

The spectral absorption of Ag-containing soda-lime-silica glasses, prepared by ion exchange under different conditions and subjected to different heat treatments, was measured in the UV and visible, Tentative Gaussian resolution analysis was performed to accurately define the component bands of the experimentally observed absorption spectra, The spectral data were used to identify the different states of silver and the shape and the spatial arrangement of the silver particles formed in the samples treated under different conditions, The data obtained were also compared with the known characteristic absorption of definite silver states, The spectra of glasses after ion exchange showed a single sharp symmetrical absorption band in the UV at 305 nm, After heat treatment, one or two additional absorption bands in the UV and visible were observed, depending on the heat-treatment conditions, The behavior of these bands-sequence of appearance, ranges of stability and intensity fluctuation, as a function of temperature and time of ion exchange and heat treatment-would suggest the following band assignment: Band at 305 nm is associated with Ag+ ions, Band at 350 nm is associated with Ag-0 (elemental Ag atoms), Band at 420 nm is associated with (Ag-0)(n) (silver crystallites, n is the number of silver atoms forming the crystallite). This band assignment is in conformity with the sequence of events widely accepted to take place during silver staining, Additional information deduced from the single absorption band associated with silver particles indicates that the silver particles are spherical in shape and isolated from each other to the extent necessary to prevent electromagnetic interaction.