The loading process of functionalized silica nanoparticles was investigated in order to obtain nanoparticles having functional groups on their surface and Near-Infrared (NIR) emission properties. The NIR emission induced by 02 loading was studied in silica nanoparticles, produced by pyrogenic and microemulsion methods, with size ranging from 20 to 120 nm. Loading was carried out by thermal treatments in 02 atmosphere up to 400 C and 90 bar. The effects of the thermal treatments on the NIR emission and on the structural properties were studied by luminescence and Raman techniques, whereas the morphological features were investigated by Transmission Electron Microscopy and Atomic Force Microscopy. Our data show that silica nanoparticles produced by pyrogenic technique can be loaded with 02 at lower temperature than the ones obtained by microemulsion and have a higher luminescence intensity due to the internal porosity of the latter. The treatments do not affect the nanosize of the microemulsion particles and provide NIR emitting probes of selected size. Post-processing surface functionalization of the pyrogenic nanoparticles does not affect their emission properties and provides high efficiency NIR emitters with functionalized surface. (C) 2013 Elsevier B.V. All rights reserved.