[en] The bright luminescence of impurity–vacancy complexes, combined with high chemical and radiation resistance, makes diamond an attractive platform for the production of single-photon emitters and luminescent biomarkers for applications in nanoelectronics and medicine. Two representatives of this kind of defects in diamond, silicon-vacancy (SiV) and germanium-vacancy (GeV) centers, are discussed in this review; their similarities and differences are demonstrated in terms of the more thoroughly studied nitrogen-vacancy (NV) complexes. The recent discovery of GeV luminescent centers opens a unique opportunity for the controlled synthesis of single-photon emitters in nanodiamonds. We demonstrate prospects for the high-pressure high-temperature (HPHT) technique to create single-photon emitters, not only as an auxiliary to chemical vapor deposition (CVD) and ion-implantation methods but also as a primary synthesis tool for producing color centers in nanodiamonds. Besides practical applications, comparative studies of these two complexes, which belong to the same structural class of defects, have a fundamental importance for deeper understanding of shelving levels, the electronic structure, and optical properties of these centers. In conclusion, we discuss several open problems regarding the structure, charge state, and practical application of these centers, which still require a solution. (reviews of topical problems)

[en] Diamond synthesis from organic materials under high pressure performed for the first time more than half a century ago is now in high demand to fit the needs of nanoelectronics and biomedicine due to the possibility of obtaining nanodiamonds of high structural perfection. The Institute for High Pressure Physics, RAS, being a pioneer in diamond synthesis in metallic solutions and unconventional media, is a recognized leader in the promotion of new trends in the synthesis of nanodiamonds free from metallic impurities. In this short review, we consider the most likely scenario of hydrocarbon carbonization with the formation of nano- and microcrystal diamonds. (conferences and symposia)

[en] We report an ¹¹B NMR study of heavily boron-doped diamond. By comparing ¹¹B spectra with those from ¹³C, we find that substitutional boron dopants are limited to 0.26 at.% in an isolated form. This observation reveals that, above the metal-insulator transition, boron dopants are incorporated into carbon sites mostly in the form of boron aggregates and suggests that, in addition to the holes in the valence band, an impurity band formed by boron aggregates plays an important role in the superconductivity in the heavily B-doped regime. A strong disorder effect deduced from Knight shift and nuclear spin-lattice relaxation rate measurements is attributed to the overlap between the intrinsic valence band and a boron impurity band.

[en] Raman and fluorescence spectroscopic techniques were used to study doped nanodiamonds synthesized at high pressure and high temperature (HPHT technique) and by chemical vapor deposition from the gas phase (CVD technique). For the CVD diamonds, a hundred-fold increase in fluorescence intensity of the silicon-vacancy centers normalized to the volume of the probe material was observed with an increase in synthesized diamond particle diameter from 150 to 300 nm. Graphitization temperature upon heating in the air significantly lower than for detonation nanodiamonds was found for the boron-doped HPHT nanodiamonds.

[en] Optical centers in diamond are possible candidates for single-photon emitters for applications in quantum communication, biology, and medicine. The study of the pressure dependence of zero-phonon lines of these centers can provide deeper insight into the electronic and structural properties of optical centers. These studies can also be useful for fine tuning the photon emission of optical centers in diamond by applying mechanical stresses. The results of ab initio calculations obtained in the study show that the pressure dependence of the position of zero-phonon lines is attributed to the electron density redistribution, whereas the effects associated with an increase in the binding energy under pressure turn out to be an order of magnitude weaker.

[en] The prospects of using individual nanodiamond particles as a source of single photons were studied for diamonds of various origin. It was shown that the single photon emitters could be produced on a base of “nitrogen-vacancy” centers in detonation nanodiamond synthesized from graphite-hexogen mixture. Studying meteoritic NDs we have found that single photon emitters based on "silicon-vacancy" centers could be realized even in molecular-sized diamond (less than 2 nm). Currently we are developing a new class of diamond materials, nanodiamonds synthesized from organic compounds at high pressure. In particular, we have demonstrated the possibility of synthesis of nanodiamond from its molecular analogue adamantane, controlling the size of crystallites in a wide range by changing synthesis temperature. A minimum size of obtained diamond particles about 3 nm was reached. Crystal structure of such diamonds is the most perfect in comparison with other classes of diamond materials, therefore they are the most promising material platform for production of single photon emitters. (paper)

[en] A composite material (CM) reinforced by diamond particles is fabricated from a mixture of cobalt and 10 wt % C₆₀ powders at a pressure of 8 GPa and a temperature of 1200–1300°C, which is close to the melting temperature of the metastable Co–C eutectic. The results of X-ray diffraction, Raman spectroscopy, and electron-probe microanalysis demonstrate that the CM consists of diamond and the Co₃C carbide. Diamond crystals are shown to grow as plates parallel to a {100} plane according to the mechanism of nonequilibrium normal growth during liquid-phase CM synthesis. The diamond particles have a hardness of 82 GPa at an elastic recovery of 95%. The structure of the synthesized cobalt-based CM with diamond inclusions ensures its ultrahigh wear resistance and antifriction properties.

[en] In this work, the effective heating of surrounding water by heavily-boron-doped nanodiamonds (NDs) under laser irradiation of visible wavelength was found. Using Raman scattering spectroscopy of aqueous suspensions of boron-doped NDs, it was found that this abnormally high heating results in the weakening of hydrogen bonds much more so (2–5 times stronger) than for undoped NDs. The property of boron-doped NDs to heat a solvent under the influence of laser radiation (1–5 W cm⁻²) opens broad prospects for their use to create nanoagents for medical oncology and local hyperthermia. (letter)

[en] Homogeneous incorporation of a small amount of binding material or modifying agent in the batch consisting of micron size particles is a problem of a composite material production process. In this work the problem is solved by deposition of a thin coating consisting of binding material on the initial powder particles by means of high-rate magnetron sputtering. The confinement of dusty particles in plasma was used in fine powder processing procedure. Composite powders based on the Al-Cu-Fe quasicrystalline particles with nickel coating were obtained. Their investigation showed that the method provides uniform incorporation of small quantities of additives (at concentration of about 3 wt. %) to fine powders. The powders were pressed at room temperature under quasi-hydrostatic conditions at high pressures. After pressing the samples were sintered in hydrogen at normal pressure. Structure and mechanical properties of the sintered samples were studied. The conditions of sintering the composite powder, which provide producing compacts with improved performance data, were established. (paper)

[en] Using two different high-pressure techniques, we have prepared boron-doped diamonds with atomic concentration of the dopant ranging from 0.04% to 4% (from 7x10¹⁹ to 7x10²¹ atom/cm³) and studied the lattice constants and thermal expansion of the diamonds in the temperature range from 90 to 300 K. Both sets of samples demonstrate the same increasing concentration dependence of the lattice parameter with maximum shift of the lattice constant about 0.011 A . We have established an abnormally high thermal expansion of the heavily boron-doped superconducting diamonds with respect to the undoped ones and a nearly linear correlation between lattice constant and critical temperature of the superconducting transition