Raman signature modification induced by copper nanoparticles in silicate glass

Composite materials formed by metal nanoclusters embedded in glasses/glazes have been produced for centuries (Roman hematinum and Renaissance alassonti, Coptic lustre-painted glass and Islamic lustre ceramics). Comparisons were drawn from Raman analyses of alkali borosilicate glasses coloured by copper as 'blue' Cu2+ (peak absorption at 750 nm), as 'colourless' Cu+ and as 'opaque red' Cu-0 (peak absorptions at similar to 420 and 570 nm). In particular, Raman analyses of copper-ruby glasses containing Cu-0 nanocrystals were performed with blue (488 nm), green (514.5 and 532 nm) and red (647.1 nm) excitation, providing information on the glass structure around the Cu-0 precipitate. Addition of europium to Cu containing glass melts yielded glasses that were dichroic; for example, a glass with 0.2 wt% Cu and 0.4 wt% Eu was red in absorbed light and blue in transmitted light. The backscattering Raman signature of the glassy silicate matrix containing copper indicated a less-polymerized network around the Cu nanocrystals/atoms than around Cu2+ or Cu+ (Raman index of polymerization similar to 1 instead of similar to 2). Strong Rayleigh scattering is measured under blue excitation for all copper-containing glasses and under red excitation for Cu-0-containing (red) glass. Copyright (c) 2005 John Wiley & Sons, Ltd.