Luminescence of oxide films during the electrolytic oxidation of tantalum

Luminescence during a constant current electrolytic oxidation of tantalum in phosphoric acid and oxalic acid is investigated. Weak anodic luminescence (galvanoluminescence) of barrier oxide films during the electrolytic oxidation is correlated to the existence of surface imperfections. Galvanoluminescence is more intense for rougher tantalum samples, higher current density, and higher electrolyte temperature. Spectral characterization of galvanoluminescence showed that there are wide luminescence bands mostly in the visible and near infrared spectral region. Small sized sparks generated by dielectric breakdown cause rapidly increasing luminescence intensity. The luminescence spectrum under spark discharging has several intensive peaks caused by electronic transitions in oxygen and hydrogen atoms.