Luminescence from nearly isolated surface defects in silica nanoparticles

A structured emission/excitation pattern, proper of isolated defects, arises in a vacuum from silica nanoparticles. The luminescence, centered around 3.0\u20133.5 eV, is characterised by a vibronic progression due to the phonon coupling with two localised modes of frequency 3c1370 cm 121 and 3c360 cm 121, and decays in about 300 ns at 10 K. On increasing the temperature, the intensity and the lifetime decrease due to the activation of a non-radiative rate from the excited state. Concurrently, the temperature dependence of the lineshape evidencesth e low coupling with non-localised modes of the matrix (Huang\u2013Rhys factor S ~ 0.2) and the poor influence of the inhomogeneous broadening. These findings outline an uncommon behaviour in the field of the optical properties of defects in amorphous solids, evidencing that the silica surface can allocate luminescent defects almost disentangled from the basal network