Absorption and photoluminescence study of Al2O3 single crystal irradiated with fast neutrons

Colour centers formation in Al2O3 by reactor neutrons were investigated by optical measurements (absorption and photoluminescence). The irradiation’s were performed at 40 °C, up to fast neutron (En > 1.2 MeV) fluence of 1.4 × 1018 n cm−2. After irradiation the coloration of the sample increases with the neutron fluence and absorption band at about 203, 255, 300, 357 and 450 nm appear in the UV–visible spectrum. The evolution of each absorption bands as a function of fluence and annealing temperature is presented and discussed. The results indicate that at higher fluence and above 350 °C the F+ center starts to aggregate to F center clusters (F2, F2+ and F22+). These aggregates disappear completely above 650 °C whereas the F and F+ centers persist even after annealing at 900 °C. It is clear also from the results that the absorption band at 300 nm is due to the contribution of both F2 center and interstitial Ali+ ions.