We studied the emission of the O2 molecules embedded in fumed silica (amorphous silicon dioxide) nanoparticles differing for diameters and specific surface. By using a 1064 nm laser as a source we recorded both the O2 emission and the Raman signal of silica. Our experimental data show that the O2 emission/Raman signal (at 800cm-1) ratio decreases with increasing the specific surface both for the as received and the loaded samples. By performing a thermal treatment (600 °C for 2h) we modified the structure and the water content of the smallest nanoparticles without observing any significant change in the O2 emission/Raman signal ratio. Our data are explained by a shell model showing that the O2 emission is essentially due to the molecules entrapped in the core of the nanoparticles, whereas the contribution due to the surface shell, having a thickness of about 1 nm, is negligible because of its high content of Si-OH groups that introduce non-radiative relaxation channels or because of the very low content of molecules trapped in this thin region.
|Numero di pagine||7|
|Rivista||JOURNAL OF PHYSICAL CHEMISTRY. C|
|Stato di pubblicazione||Published - 2013|
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