Evgeny A. Vasilev

The object of the present study is a single-crystal multisectorial diamond plate synthesized by HPHT technique in Fe-Co environment with boron and nitrogen getters. These undoped type IIa diamonds find extensive use in X-ray optics, UV photodetectors, and ionizing radiation detectors, all of which necessitate precise control over the samples’ impurity content. Complementary non-destructive optical and electrical techniques were employed in a comprehensive study to assess the background concentration of boron in sectors , , of the plate. The discussion addresses the features of the application of these methods for detecting extremely low concentrations and the spatial heterogeneity of the measured values across the sectors of type IIa diamond plates. UV transmission spectra near the fundamental edge were obtained and mathematical modeling was performed to study exciton and phonon effects affecting the diamond absorption in this spectral range. The room temperature FTIR spectra was shown to be insufficiently sensitive for controlling impurities in the plate; the spectra measured at the liquid nitrogen temperature allowed us to determine the boron concentration in the sector as 3.5 ppb (6.3×1014 cm–3). The differences in current-voltage characteristics measured in various points of the plate are discussed. The performed capacitance-voltage measurements showed a strong dependence on the test signal frequency and enabled the assessment of low free charge concentrations (at the level of 1015 cm-3 and below, with the value varying by plate sector and frequency). The activation energy of boron was assessed by electrical measurements in DC (370 meV) and AC (345 meV) modes, the differences in the obtained values are discussed. Overall, this study shows that electrical measurements provide a non-destructive approach capable of determination background impurity content in specially undoped single-crystal diamond below the limits of conventional optical methods.

A specially grown boron-doped HPHT diamond with low nitrogen content was treated and investigated in order to reveal possible positively charged defects. Two multisector plates of the diamond were irradiated with 3 MeV electrons at a fluence of 1018 cm2, and one of them was then annealed at 1200 °C. The samples were studied by photoluminescence (PL) and absorption spectroscopy in the UV/VIS and IR spectral ranges. The sector with 4.4 ppm of boron has a set of the most intense PL systems. The sector with 220 ppm of boron shows no sharp PL features either after irradiation and annealing. The PL spectra of the irradiated diamond reveal basic radiation-induced systems 3H and GR1 and a few sharp lines, the most intense of which are 491.6, 635.6, 666.0, and 732.3 nm. After annealing, the systems at 491.2, 517.4, 575.0, and 784.8 nm and sharp lines at 775.9 and 781.2 nm dominate the spectra of and sectors. The 784.8 nm system appears in all sectors; possibly, it is a signature of the boron-vacancy complex. The 517.4 nm system, previously attributed to NV+, appears to be associated with more intense, very narrow lines at 775.9 and 781.2 nm. The 523.7 nm system was found to have a state with ZPL 520.9 nm, with the possibility of their controlled switching. These systems have analogues with zero-phonon lines at 486.3 and 488.9 nm. Thus, B,N co-doped diamond has a number of previously unreported PL systems due to positively charged intrinsic and nitrogen-vacancy defects.

This paper is focused on tourmaline from quartz veins associated with rare-metal granites of the Severny (Northern) Pluton, Chukotka, within which the Erguveem, Kekurnoe, Stremitelnoe, and Glubokoe tin deposits have been discovered, with the giant Pyrkakai tin deposit located close to the south border of the pluton. Tourmalines from four host types have been described: replacement lenses (RL) in pegmatoid pockets and three types of quartz veins cutting through granite rocks of the pluton. Tourmalines have been studied with electron microprobe, laser ablation inductively coupled plasma mass-spectrometry (LA-ICP-MS), Mössbauer spectroscopy, and Raman spectroscopy. The tourmalines are classified as fluor-dravite, dravite, oxy-dravite, fluor-schorl, schorl, oxy-schorl, foitite, oxy-foitite, magnesio-foitite, and ferro-bosiite. Ferro-bosiite from the type III veins is Sn-bearing. Leading substitutions in the tourmalines are Al + ^WO^2– ↔ Fe²⁺ + ^WOH^–(F^–), X-site vacancy + Al ↔ Na + Fe²⁺, and Fe³⁺ ↔ Al. An increase in the Fe³⁺/Fe_tot value from 10% in the RL tourmalines to 14% in the type III vein tourmalines along with abundant ferro-bosiite in the latter, indicate an increase in oxidation potential. This increased oxidation potential possibly contributed to a cassiterite deposition. Raman data are consistent with composition of the tourmalines.

Using a wide complex of mineralogical-geochemical and isotope-geochemical methods we studied, a unique series of samples of fossil camels’ bone remains taken from Eurasian localities from the northwestern Black Sea region to western Transbaikalia and Mongolia, dated in the chronological range from the Late Miocene (6 Ma) until the 14th century AD. The obtained results indicated the mineralogical and geochemical properties of fossil bones as very effective way of ecological and climatic reconstructions and interpretation of the evolutionary history of mammals.

Diamond crystals of various morphological types, including carbonado, were studied by the electron backscatter diffraction method. Cases of inhomogeneities of different natures were revealed: interpenetrant and mechanical twins, incoherent intergrowth, and splitting growth. Differences in the distribution pattern of boundary angles for different types of inhomogeneities have been shown: predominantly discrete in intergrowths, continuous distribution of low-angle boundaries in ballas diamonds, and continuous random distribution in carbonado. It has been shown that Rose channels in diamond arise as a result of etching at the intersection of mechanical twins. The revealed mechanical twins have a thickness of 60–600 nm.

Research subject. The article presents the results of studying 500 diamond crystals from the core of exploration boreholes of crater and diatreme facies of the upper part of V. Grib kimberlite pipe. Crystals from tuffs and tuffites (crater), tufobreccia, autolith kimberlite breccia and porphyry kimberlite (diatreme) were analyzed separately. aim. To carry out a morphological and spectroscopic study of diamonds from V. Grib pipe. Materials and Methods. An VERTEX-70 spectrometer with a Hyperion 1000 microscope was used to determine the total nitrogen concentration and the share of nitrogen in the form of B defects (N_BS), the absorption coefficients of the “platelet” bands B', 3107 cm^-1. Images of photoluminescence (PL) were recorded at 360 nm excitation by an ALROSA VIEW PRO device, in order to detect inhomogeneities and color of PL. The PL spectra were recorded by a Horiba FL-3 spectrometer with an excitation of 350 and 450 nm at 300 K and by an InVia Renishaw spectrometer with an excitation of 405, 488 and 787 nm at 77 K. Results. The distribution of diamonds in terms of nitrogen concentration and NBS is specific; about 50% of the crystals are located along one isotherm, the proportion of low-nitrogen crystals is 5%. The PL spectra of 25% of crystals showed the lines of 883/885 nm of an elementary Ni-containing defect. Most crystals with this defect have less than 400 ppm of nitrogen, but they occupy the entire range according to NBS. This system is found in the spectra of 76% of twins and intergrowth; the latter are of 36% of diamonds with the lines 883/885 nm. The studied diamonds differ from those found in M.V. Lomonosov deposit in terms of a much lower content of crystals of cubic habitus (2 and 15%), a lower degree of dissolution (octahedra, respectively, 33 and 15%), a low proportion of colored stones, as well as a wide range of nitrogen concentration and NBS. Conclusion. The revealed features indicate the specific growth conditions of diamonds from V. Grib deposit, which differed from those of diamonds from other kimberlitic bodies of the East European, Siberian platforms and the Urals. The high proportion of low-nitrogen crystals and Ni-containing diamonds is a possible indicator for the presence of large CLIPPIR-type crystals.

Tightly focused 515-nm, 0.3-ps laser pulses modify in a laser filamentation regime the crystalline structure of an Ib-type high-pressure, high-temperature (HPHT) synthesized diamond in a thin-plate form. The modified microregions (micromarks) in the yellow and colorless crystal zones, possessing different concentrations of elementary substitutional nitrogen (N) impurity atoms (C-centers), exhibit their strongly diminished local IR absorption (upon correction to the thickness scaling factor). Simultaneously, local visible-range (400–550 nm) absorption coefficients were increased, and photoluminescence (PL) yield was strongly enhanced in the broad range of 450–800 nm. The strong yellow-red PL enhancement saturates with laser exposure, implying the complete conversion of C-centers into nitrogen-vacancy (NV^0,−) ones due to the laser-induced generation of Frenkel “interstitial-vacancy” I–V carbon pairs. The other emerging blue-green (>470 nm) and green-yellow (>500 nm) PL bands were also simultaneously saturated versus the laser exposure. The observed IR/optical absorption and PL spectral changes enlighten the ultrashort pulse laser inscription of NV⁰⁻-based quantum-emitter centers in synthetic diamonds and enable the evaluation of the productivity of their inscription along with the corresponding I–V generation rates.