Fumed silica with specific area of 295 m²/g was carbonized by successive procedures of chemical modification by phenyltrimethoxysilane followed by annealing in inert atmosphere up to 650 ^oC. Strong ultraviolet and visible photoluminescence was observed in the samples after chemical modification and thermal annealing. Emission, excitation, kinetics and photo-induced bleaching effects were investigated by steady state and time-resolved photoluminescence spectroscopy. Interatomic bonds were studied by infrared transmission spectroscopy. It has been shown that ultraviolet photoluminescence in chemically modified fumed silica is associated with phenyl groups while near ultraviolet and visible emission in annealed samples originates from inorganic pyrolytical carbon precipitates dispersed in silica host matrix. Two types of emission bands were identified depending on the annealing temperature: one is in the near UV and another is in the visible range. The relative contribution of these bands depends on samples preparation. All the obtained results have been compared with those observed in fumed silica carbonized using other carbon precursors and treatment procedures. It has been found that these two bands can be observed irrespective to the carbonization procedure. Based on the emission/excitation analysis of these two bands, as well as on correlations with the synthesis conditions, a structural-energy concept of light-emitting centers has been proposed. According to this model, the light-emitting centers are associated with sub-nanometer carbon clusters that can be bonded or adsorbed on the silica surface. It is assumed that the energy of emission photons is determined by the presence or absence of a chemical bond between the emitting clusters and silica surface.

A detailed (S)TEM-EELS study has been performed to check these points. By doing so, we have confirmed the presence of 2-6 nm carbon nanoclusters, which are not evenly distributed at the surface of the silica nanoparticles. These carbon nanoclusters are mostly amorphous although they possess some degree of graphitization and local order; the fraction of sp² carbon in these nanoclusters has been estimated to be close to 80 %.

Spectral distribution of light emission in visible range of black body at 6000 K (corresponding to natural day-lighting) and PL of the samples annealed at 600 ^oC (excitation 355 nm) is almost identical. Spectral properties of the emission (in terms of RGB concept - correlated color temperature) can be easily tuned by variation of synthesis procedure. Such light emission properties of environment friendly single component phosphor make them very attractive for artificial white light sources like white LEDs with near-UV excitation or compact fluorescent lamps.