Photoluminescence characterization of sol-gel prepared low density silica samples

By exciting with synchrotron radiation in the 4-10 eV range the emission properties of sol-gel synthesized porous silica at room temperature and at 8 K are investigated. The modifications of the ultraviolet emission in the range 3.7-4.2 eV excited at different energies (5.64, 6.20, 6.53, and 6.89 eV) support the hypothesis of the contribution of two emitting centers. In particular the two emissions are spectrally resolved when exciting at 5.64 eV and a blue shift of the emission peak is reported as the excitation energy increases. The analysis of the decay times indicates that the two centers are temporally resolved with the 5.64 eV excitation both at room temperature and at 8 K and allows to estimate lifetimes of about 3 and 18 ns. When exciting at 6.53 eV, the larger relative contribution of the 4.0 eV band does not allow to efficiently resolve the two decay times and the estimated life time of the 3.8 eV band is shortened.