Sapphire crystals were implanted with 380 keV Nb~+ ion to a dose of 5 x 10~(16) ions/cm~2. The behaviors of the radiation damage produced by ion implantation followed by annealing with a series of steps from 500 to 1100°C at reducing atmosphere were investigated using optical absorption, and XPS measurements. It has been found that the implanted niobium in sapphire is in different local environments with different charge states after annealing. The results of optical density (OD) from the bands based on the well known F-type centers with annealing temperature and time show that the annealing behaviours of the radiation damage can be divided into different stages due to different mechanisms.
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