Distribution of nickel related luminescence centers in HPHT diamond

We have observed the distribution of luminescence centers of pre- and post-annealed HPHT diamond crystals grown from Ni with and without Ti as a nitrogen getter using microscopic photoluminescence spectroscopy excited by a 325 nm He-Cd laser. It is demonstrated that six luminescence centers, which are expected to be Ni-related, are present in the crystals with different distribution. They are a center having the 418 nm, the 2.56 eV, the S2 and S3 centers, and two broad bands with maximums between 500 and 550 nm. The different distributions indicate that each center are ascribed to defects with different structure and concentrations of both nickel and nitrogen impurities. (C) 1999 Elsevier Science S.A. All rights reserved.