EPR spectra of separated pairs of substitutional nitrogen atoms in diamondwith a high concentration of nitrogen

Electron paramagnetic resonance (EPR) measurements are reported in syntheti c diamonds grown in an Fe-Ni-C solvent/catalyst system at 1750 K, under sta bilizing pressure, by the temperature gradient method. Such diamonds are kn own to have high concentrations of nitrogen. EPR spectra have been found in three well-separated regions. The first of these spectra consists of a fam ily of lines around the EPR spectrum of the P1 center (isolated N-s). The s econd spectrum consists of a family of weak Lines at about one-half of the P1 magnetic held. The third consists of a family of weak lines at about twi ce the P1 magnetic field. The first spectrum is attributed to three defect centers, named NOC1, NOC2, and NOC3 (NOC stands for the Novosibirsk-Oxford collaboration); each one of the centers corresponds to a pair of N-s atoms with different separations. The second spectrum, named NOC 1, is also attri buted to separated pairs of N-s atoms, but is a superposition of spectra fr om all pairs with separation greater than about 0.7 nm. The third spectrum is attributed to isolated P1 centers which were resonated by a two microwav e photon transition. [S0163-1829(99)09031-1].