Photoluminescence and diffusion properties of O2 molecules in amorphous SiO2 nanoparticles

An experimental study by Raman and Photoluminescence (PL) spectroscopies on the emission and diffusion properties of O2 molecules in amorphous SiO2 nanoparticles of commercial origin with diameters from 14 to 40 nm is reported. Stationary and time resolved PL measurements have been carried out to characterize the Near Infrared (NIR) emission at 1272 nm of O2. Emission features similar to those of bulk silica systems with a sharp PL band and excitation channels in the NIR, at 1070 nm, and in the visible, at 765 and 690 nm are found, with peculiarities arising from embedding O2 in nanostructures.The study of the NIR PL lifetime as a function of temperature down to 10 K enabled to reveal the presence of non radiative processes competitive to the radiative channel and to the non-radiative one already highlighted and related to high energy vibrational modes of matrix or of impurity sites. By detecting the O2 content of nanoparticles, the dynamics of diffusion in the low temperature range from 98°C up to 177°C has been characterized. The applicability of Fick’s theory has been tested, determining the diffusion coefficients and evidencing some peculiarities detectable in the nanosystem.