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 NV 0 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), NV 0 , 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) Å corresponds (within the measurement error) to the maximum value known for these diamonds.