Optically active centers in diamond as-grown at temperatures 1200-1350°C

Diamonds were grown in the vicinity of the “diamond‐graphite” equilibrium state by the spontaneous crystallization method to study the creation of defects and crystalline imperfections. Crystals were synthesized in the graphite‐Ni‐Mn system. Raman and luminescence spectroscopy, electron microscopy, and optical absorption spectroscopy were used for diamond crystal inspection. Diamonds were classified into three groups: (1) black, nontransparent, curved, flat‐faced crystals; (2) dark or black semitransparent crystals of cubic habit with faceting of the cube vertices by (111) planes; (3) amber‐yellow crystals showing a cubic‐octahedral habit. The yellow crystals revealed the infrared (IR) absorption spectra within the range of 800–4000 cm‐1 that are peculiar for diamonds of the 1a group. IR spectra displayed a number of additional absorption peaks for black semitransparent crystals. A marked peak at 2835 cm‐1 and a less pronounced peak at 2919 cm‐1 unambiguously demonstrate the presence of hydrogen. An intensive absorption in the range of 800–1100 cm‐1 with a maximum at 969 cm‐1 may be explained by both the presence of hydrogen and extended defects, taking into account the data arrived at by cathodoluminescence, emission spectra, and Raman spectroscopy. For the first time, the narrow peak at 1332 cm‐1, unknown for mined diamonds and observed in flame‐chemical vapor deposition (FL‐CVD) diamond films, was revealed in diamonds synthesized under high pressure. The presence of peaks with maximum at 2919, 1252, and 1332 cm‐1 in the IR spectra of the black diamonds and FL‐CVD diamond films indicated a certain similarity in diamond formation for high‐ pressure and vapor deposition techniques and an important role of hydrogen in high‐pressure diamond growth. The source of hydrogen is probably graphite used in the synthesis. The increase in diamond synthesis temperature decreases the probability of hydrogen capture and provides a better crystal quality. Cathodoluminescence scanning electron microscopy demonstrated the spatial distribution of luminescence centers on different diamond crystal faces. Some crystal fragments emit A‐band (420–460 nm) and have well‐faceted faces that confirm their high perfection and quality that are close to natural diamonds.