Luminescence centers in pre-annealed and post-annealed HPHT crystals, grown from Ni with and without Ti as a N getter, were observed by means of microscopic photoluminescence spectroscopy; as excited by 325nm He-Cd laser light. It was demonstrated that 6 luminescence centers (41.8nm, 2.56eV, S2, S3, and 2 broad bands with maxima between 500 and 550nm), which were expected to be Ni-related, were variously distributed. The various distributions indicated that each center could be attributed to defects with differing structures and concentrations of both Ni and N impurities.

Distribution of Nickel Related Luminescence Centers in HPHT Diamond. H.Kanda, K.Watanabe: Diamond and Related Materials, 1999, 8[8-9], 1463-9