Photoluminescence and diffusion properties of O2 molecules in amorphous SiO2 nanoparticles

An experimental study by Raman and Photoluminescence(PL) spectroscopies on the emission and diffusionproperties of O2 molecules in amorphous SiO2 nanoparticlesof commercial origin with diameters from 14 to 40nm is reported. Stationary and time resolved PL measurementshave been carried out to characterize the NearInfrared (NIR) emission at 1272 nm of O2. Emission featuressimilar to those of bulk silica systems with a sharpPL band and excitation channels in the NIR, at 1070 nm,and in the visible, at 765 and 690 nm are found, with peculiaritiesarising from embedding O2 in nanostructures.The study of the NIR PL lifetime as a function of temperaturedown to 10 K enabled to reveal the presence ofnon radiative processes competitive to the radiativechannel and to the non-radiative one already highlightedand related to high energy vibrational modes of matrix orof impurity sites. By detecting the O2 content of nanoparticles,the dynamics of diffusion in the low temperaturerange from 98°C up to 177°C has been characterized.The applicability of Fick’s theory has been tested, determiningthe diffusion coefficients and evidencing somepeculiarities detectable in the nanosystem.