Influence of preparating conditions on the luminescence of pure silica coatings

SiO2 coatings prepared by sol-gel technique show an UV-Visible luminescence with a maximum centered at about 3.4 eV (365 nm). The emission spectrum can be decomposed into two Gaussian shape bands, centered at 3.35 eV (370 nm) and 3.0 eV (415 nm), respectively. The corresponding excitation spectrum shows a band centered at 3.85 eV (320 nm). In order to clarify the origin of that luminescence, a study as a function of precursors used for coatings preparation was done, as well as a function of thermal treatments carried out during densification. Moreover, the presence of organic matter in the coatings prior to densification, modifies their luminescent properties. So that, some variations of the luminescence spectrum could be understood as the result of both changes in the residual organics of coatings and variations in the surplus oxygen content.