Vibronic structures in the visible luminescence of silica nanoparticles

We report the spectroscopic characterization in air and in vacuum atmosphere of the visible luminescence related to silica surface defects. Time resolved photoluminescence technique allows to discern two contribution: the first one, observed both in air and in vacuum, is the well known blue band, peaked around 2.8 eV decaying in \u3c4~5 ns; the second, only observed in vacuum, is a structured emission in the violet range characterized by two vibronic progressions spaced 1370 cm-1 and 360 cm-1 decaying in \u3c4~90 ns. On the basis of these spectroscopic properties, we revise the structural models of luminescent defects