Ion irradiation effect of alumina and its luminescence

The luminescence spectra of single crystalline alpha-alumina and ruby which has 0.02% of Cr2O3 as a impurity, induced by 200 keV He+ and Ar+ irradiation were measured at room temperature as a function of irradiation dose. The analysis of the measured spectra showed the existence of three main luminescence features in the wavelength region of 250 to 350 nm, namely anionic color centers, F-center at 411 nm and F+-center at 330 nm and a band observed around 315 nm. As alpha-alumina was irradiated with He+, F-center and F+-center luminescence grew and decayed, but the behaviors of those were different from each other. It seems that a concentration quenching occurred on the F-center luminescence in the dose range above 1x1014 He/cm2. Furthermore, F-center luminescence was strongly suppressed in ruby, compared with that in alumina. On the other hand, the luminescence band around 315 nm appeared only in the early stage of irradiation and did not show its growth part. The dose dependent behavior was similar to that of Cr3+ emission at 695 nm (R-line) in ruby in both cases of He+ and Ar+ irradiation. Based on the experimental results mentioned above, the processes of defect formation and excitation in alumina in the early stage of ion irradiation will be discussed. (author)