We report four new EPR spectra found in high-pressure synthetic diamonds wi
th high nitrogen content, grown using nickel, and annealed at 1600 degrees
C. Analyzing the complex spectra around g approximate to 2 two trigonal and
two orthorhombic defects, all with S = 1/2, were identified from the angul
ar dependence and the different saturation behavior of the transitions. Bes
ides optical and EPR investigations reveal several centers which have been
previously ascribed to defects containing nickel and nitrogen. However, nit
rogen is not involved in the new centers, since no evidence of an N-14 hype
rfine structure could be found. Possible relations of the new defects with
Ni are discussed. (C) 1999 Elsevier Science B.V. All rights reserved.