The optical and magnetic properties of Ni-related defects in as-grown diamond were reviewed. Published, and new, data on the problem of negatively charged substitutional Ni were presented. It was shown that the 2.51eV absorption band occurred at Nis-, while spin–orbit and Jahn–Teller interactions played important roles in the optical properties of the defect.

Nickel-Related Defects in Diamond - the 2.51eV Band. M.H.Nazaré, J.C.Lopes, A.J.Neves: Physica B, 2001, 308-310, 616-20