RADIATION-DAMAGE IN AL2O3 CRYSTALS IMPLANTED WITH 3.8 MEV FE2+ IONS

Sapphire (alpha-Al2O3) crystals were implanted with 3.8 MeV Fe2+ ions to fluences of 0.5 x 10(16) and 2 x 10(16) cm-2. The sample face was perpendicular to the c-axis. The radiation damage produced by the implantation was investigated using optical and electron paramagnetic resonance (EPR) techniques. The former encompassed optical absorption and luminescence. The predominant defect detected optically was the oxygen vacancy with two electrons (F center), identified by an absorption peak at 6.2 eV (approximately 200 nm). The paramagnetic oxygen vacancy with one electron (F+ center) absorbs at 4.8 eV (approximately 260 nm) and was identified by EPR. Divacancies in various charge states were present in much lower concentrations and could not be unambiguously identified by optical absorption. Instead, they were detected by the highly sensitive luminescence measurements. Upon isochronal annealing between 500 and 1200 K, the concentration of the F center decreased monotonically. No evidence of the F+ center was found after annealing at 800 K.