The cathodoluminescence intensities of F+ centers in Be-diffusion-post-treated natural sapphire and synthetic sapphire were found to increase substantially under continuous irradiations with 15keV electrons using constant incident currents ranging from 0.1 to 2μA. This was represented approximately by an exponential saturation function of the electron fluence. The efficiency of F+-center cathodoluminescence emission at room temperature was higher in synthetic sapphire than in Be-treated natural sapphire. Whereas the cathodoluminescence intensity of Be-treated samples exhibited little temperature dependence, that of the synthetic sapphire decreased by about an order of magnitude upon decreasing the specimen temperature from room temperature to 85K. In addition, time-resolved photoluminescence data found for the 420nm emission revealed a relatively shorter lifetime of the Be-treated natural sapphire specimen. These results indicated that natural sapphire which was successfully post-treated with Be diffusion had a slightly but substantially poorer crystalline quality than did synthetic sapphire.

Different Behaviors of F+ Centers due to Electron Beam Irradiations between Synthetic Sapphire and Be-Diffusion-Treated Natural Sapphire. B.H.Lee, T.Teraji, T.Ito: Journal of Crystal Growth, 2006, 292[2], 546-9