Reversible transformation of silver oxide and metallic nanoparticles inside a relatively porous silica film has been established. Annealing of Ag-doped films in oxidizing (air) atmosphere at 450 C yielded colorless films containing AgOx. These films were turned yellow when heated in H-2-N-2 (reducing atmosphere) due to the formation of Ag nanoparticles. This yellow coloration (due to nano Ag-0) and bleaching (conversion of Ag-0 -> Ag+) are reversible. Optical and photoluminescence spectra are well consistent with this coloration and bleaching. The soaking test of the air-annealed film in Na2S2O3 solution supports the presence of Ag+. Grazing incidence X-ray diffraction and transmission electron microscopy studies reveal the formation of Ag-oxides and Ag nanoparticles in the oxidized and reduced films, respectively. (C) 2008 Elsevier Ltd. All rights reserved.