Ultraviolet excitation of photoluminescence of porous silica under vacuum conditions

The optical properties of porous sol–gel silica are investigated by measuring the absorbance spectrum in the vacuum ultraviolet energy range and the excited photoluminescence. The emission spectrum shows a luminescence with two maxima at about 3.5 eV and <3.0 eV depending on the excitation energy. We observed a decrease of the 3.5 eV emission band with increasing irradiation time with the samples in vacuum. The modification induced on the material cannot be recovered by exposing the samples to the ambient atmosphere. We ascribed the measured photoluminescence to OH-related surface centers whose structure is modified by the concomitant action of vacuum conditions and ultraviolet irradiation time.