Optical Analysis of Nb⁺ Implanted Sapphire Before and After Annealing

Sapphire crystals with different orientations were implanted with Nb⁺ ions in different conditions and annealed at reducing atmosphere. Optical analysis results show that the main optical absorption bands lay in the higher energy sector for all the samples. The absorption curves were evaluated by Gaussian fitting based on the well known F-type centers, which were confirmed by luminescence measurements. The results of Gaussian fitting show that there are F center, F⁺ center, F₂ center, F⁺₂ center and F²⁺₂ center in sapphire implanted with Nb⁺ ions. After annealing at different temperature, all kinds of color centers decrease, the higher the temperature is, the more the defects decrease. The stabilization of the defects also relates with the implantation temperature. In addition, the optical density of luminescence peak at about 700 nm shows different changing with the changing of the exciting light’s wavelength.