An in situ optical microspectroscopy investigation of the growth and oxidation of silver nanoparticles (NPs) embedded in SiO2 thin films deposited on soda-lime glass has been conducted in real time during thermal processing in air. Variation of Ag NP size is followed by fitting of surface plasmon resonance (SPR) with spectra calculated by Mie theory, and analysed concurrently with the time evolution of SPR peak intensity. The NP transformations appeared to be temperature and time dependent. Silver NPs were indicated to grow at relatively high temperatures (e.g. 600 degrees C) due to Ostwald ripening, followed by a plateau and a gradual decrease in size resulting in SPR vanishing due to oxidation. The three phases were well separated in time. Oxidation appeared dominant at lower temperatures (e.g. 400 degrees C) as indicated by a continuous decrease in Ag particle size. The product of Ag NP oxidation was revealed by photoluminescence spectroscopy as single Ag+ ions. Furthermore, the data indicated that: (i) Ag+ ions are formed during heat treatment under an Ag/Ag+ redox equilibrium; (ii) the ions diffuse from the SiO2 matrix towards the soda-lime substrate where they stabilize; and (iii) the continuous removal of these ions from the matrix is necessary in order for the equilibrium to be displaced towards oxidation. (C) 2010 Elsevier Ltd. All rights reserved.