The luminescence of sapphire subjected to the irradiation of energetic hydrogen and helium ions

The luminescence of alpha-Al2O3 during He+ and H+ irradiation was measured in the 190-820 nm wavelength range. The luminescence evolution with the ion fluence exhibits two behaviours : (i) at low fluence, the amount of F+ centres increases; (ii) at high fluences, these defects are completely (F centres) or partially (F+ centres) annihilated. This phenomenon results from two concomittant mechanisms : a conversion between F and F+ defects and a destruction of both luminescent species resulting from the radiation-induced damage. By using a simple model we have determined the cross sections associated with creation (sigma(c)) and annihilation (sigma(a)) of the F+ centres. The irradiated samples were also investigated by cathodoluminescence and Auger electron spectroscopy. A higher concentration of structural defects and F+ centres is evidenced at the sample area previously irradiated by ions, leading to an unsteady regime of the surface potential under electron excitation.