Interstitial O2 distribution in amorphous SiO2 nanoparticles determined by Raman an Photoluminescence spectroscopy

The O2 content and emission properties in silica nanoparticles after thermal treatments in oxygenrich atmosphere have been investigated by Raman and photoluminescence measurements. Thenanoparticles have different sizes with average diameter ranging from 7 up to 40 nm. It is found thatO2 concentration in nanoparticles monotonically increases with nanoparticles size. This finding isindependent on the measurement technique and evidences that oxygen molecules are not present inall the nanoparticles volume. This dependence is interpreted on the basis of a structural model fornanoparticles consisting of a core region able to host the oxygen molecules and a surface shell offixed size and free from O2.