The influence of HTHP treatment on the OK1 and N3 centers in natural diamond crystals

The structures of nitrogen-containing paramagnetic centers OK1 and N3 have not been unambiguously determined yet. In this paper, we will present data on the influence of high temperature annealing on the paramagnetic centers OK1 and N3 in diamond. A series of natural colored diamond crystals of cubic habit containing paramagnetic centers OK1 and N3 was studied by electron paramagnetic resonance (EPR), luminescence, and IR spectroscopies. It was found that annealing at temperatures above 2470 K led to the transformation of N3 paramagnetic centers into OK1 paramagnetic centers. Previous work has showed that a temperature in excess of 2400 K are often associated with a local environment change of tetrahedral to octahedral for impurities with large atomic radii. We report a correlation with the intensity of the optical 635.7 nm system and the concentration of the N3 EPR center. However, on stepped annealing 635.7 nm was removed before the N3 EPR center. From the analysis presented, we propose that the N3 EPR center and the 635.7 nm optical system are the manifestation of various defects formed by one impurity atom.