NEW DATA ON THE STRUCTURE OF DIAMOND SINGLE CRYSTALS WITH A HIGH CONCENTRATION OF NITROGEN CENTERS

Natural diamonds with a high concentration of nitrogen centers (Kumdykul deposit, North Kazakhstan) are studied. According to the IR spectroscopic data, the concentration of nitrogen C- and A-centers is several hundred ppm at a total concentration above 1000 ppm. At 532 nm excitation the low-temperature photoluminescence (PL) spectra demonstrate dominant luminescence in the 638 nm system, which is caused by negatively charged nitrogen-vacancy (NV-) pairs. The latter is a consequence of a high concentration of donor nitrogen atoms. One electron is transferred from a donor nitrogen atom to the NV pair. Broad bands with maxima at 530 nm and 590 nm correspond to H3 and 575 nm systems: NVN and NV0 complexes. Strong broadening of the diamond Raman line up to 6.5 cm(-1) is observed along with the broadening of 503.2 nm, 575.0 nm, and 638.0 nm zero-phonon lines in the PL spectra up to their complete disappearance. This is explained by a high concentration of NVN(H3), NV0, and NV- centers, respectively, as well as structural defects. The unit cell parameters of single crystals are refined by the original procedure. The obtained value of 3.5675(1) angstrom corresponds (within the measurement error) to the maximum value known for these diamonds.