Here we report on the production of an Ag2SO4/Ag2O mixed-grain powder during the anodization of Ag foil in a HF-H2SO4 electrolyte. We propose that there are three competing reactions during the anodization process: (i) the production of Ag2O at the Ag foil anode surface from the presence of water in the electrolyte, (ii) the dissolution of the Ag2O in the presence of HF releasing Ag+ ions, (iii) the precipitation of Ag+ and SO42- ions, as Ag2SO4 on the Ag foil anode surface. This co-precipitation/dissolution process ultimately results in a mixed-grain powder. We then show that the Ag2O embedded within the mixed-grain is photo-decomposed to produce highly fluorescent silver nanoclusters (Ag-n) which decorate the Ag2SO4 crystals. The Ag2SO4 salt offers a stable matrix for the photo-decomposed Ag-n nanoclusters to emit their strong fluorescence. (c) 2013 Elsevier B.V. All rights reserved.