Near-Infrared Emission of O₂ Embedded in Amorphous SiO₂ Nanoparticles

Properties of HO 2 • radicals induced by γ-ray irradiation in silica nanoparticles

“…Here we can extend the use of this procedure to silica nanoparticles considering some multiplying factors to take into account quantum yield variations, as recently reported [24]. They are due to the different life times of the various nanostructured materials studied here with respect to bulk silica [17]. Furthermore, the use of the procedure suggested by Kajihara et al [8] presents a further difficulty which is accentuated by studying nanostructured samples: the Raman band choosen as reference is one of the less intense and consequently the experimental uncertainty associated to the estimation of its intensity is very large.…”

“…The powders were pressed in a hydraulic press to obtain selfsupporting tablets not altering the structural properties of the fumed silica samples [21,22]. All the pristine materials were preventively loaded with O 2 molecules by treating them at T~200°C in oxygen atmosphere (P = 50 bar) for 11 h [17]. After loading, a natural outgassing process was observed.…”

“…These facts have leaded us to improve the method by making some changes. We have taken advantage from the work done by Agnello et al [17,24] where interstitial O 2 concentrations were estimated in several a-SiO 2 nanostructured samples following the method suggested by Kajihara et al [8] but considering the differences, reported above or in the following, between nanoparticles and bulk silica. In this context it is worth noting that previous studies have shown that the estimations of O 2 absolute concentration by optical measurements are in agreement within 50% [8,24].…”

“…We can express the factor K i as the ratio between a quantity α (here considered indipendent from the features of the nanoparticles [17][18][19]22]) and the O 2 PL life time τ i :…”

“…In fact, to detect and evaluate the amount of interstitial O 2 one can make use of the electronic transition in O 2 from the first excited state 1 Δ g to the ground state 3 Σ g − . This transition gives rise to an infrared (IR) photoluminescence (PL) band at~1272 nm that a Raman spectrometer equipped with a Nd:YAG laser source at 1064 nm can detect [8,[16][17][18][19][20].…”