The behavior of the radiation damage of sapphire crystal, produced by implantation with 380 keV Nb⁺ ion followed by annealing in a series of steps from 500 to 1100°C at reducing atmosphere, was investigated in optical absorption and XPS measurements. It is found that the implanted niobium in sapphire is in different local environments with different chemical states after the annealing. The changes in optical density (OD) from the bands, based on the well known F-type centers, show that the annealing behavior of the radiation damage may be divided into different stages due to different mechanisms.