Features of the defect-impurity composition of diamonds from the northern Istok and Mayat placers (Yakutia) according to EPR, IR, and luminescence data

Diamonds from placers in the northern provinces of the Siberian Platform attract attention not only due to the unsolved problem of their sources but also due to the variety of properties they exhibit. In this work, electron paramagnetic resonance (EPR), infrared (IR), and photoluminescence (PL) methods were used to study cuboid diamonds from Istok (25 diamonds of Ib-IaA type) and dodecahedron diamonds from Mayat (21 diamonds of IaAB type) placers. The main impurity defects in the crystals studied are nitrogen, nitrogen-titanium, and oxygen-containing centers. The total amount of nitrogen in the form of C (P1 in EPR nomenclature), A, and B centers ranges from 34 to 903 ppm. For 19 out of 25 crystals from the Istok placer, the N3 titanium-related center is observed in the EPR spectra, but only one optical system with zero-phonon line (ZPL) at 635.7 nm is detected in the PL spectra in most cases. It can be assumed that the absence of an accompanying system with ZPL at 440.3 nm is due to its quenching by other centers in these crystals. For 12 out of 21 crystals from the Mayat placer, photoluminescence of oxygen-containing centers in the region of 600–800 nm in the form of a series of equidistant bands with an interval of ~ 31 meV was revealed. A comparison of the EPR and PL data has shown that this red broad band is not correlated with titanium-nitrogen paramagnetic centers OK1 and N3. Thus, the results obtained for diamond crystals from the Istok and Mayat placers show no connection between the N3 and OK1 paramagnetic centers and band in the 600–800 nm region, which questions the presence of oxygen in the structure of the N3 and OK1 centers. The nickel-nitrogen centers were found in crystals from the Mayat placer testifying about the peridotitic paragenesis of these diamonds.