Spectroscopic features of brown diamonds from Ural placers

Abstract

Research subject. Brown diamond crystals from placers of the western slope of the Middle/Northern Urals. Aim. Study of the defect-impurity composition of a sample of brown diamonds from the placers of the western slope of the Middle/ Northern Urals. Methods. In this work, special attention is paid to the analysis of the characteristic spectroscopic features of defects in diamonds from the placers of the western slope of the Middle/Northern Urals using photoluminescence and IR spectroscopy. Results. The studied diamonds from placers of the Middle/Northern Urals are round isometric crystals of a dodecahedral (tetrahexahedral) habitus. According to the results of luminescence (PL) and infrared spectroscopy, three groups of crystals can be distinguished: (i) medium and high nitrogen crystals with low aggregation and dominant defects H3 and 490.7 nm in the PL spectra; (ii) medium and high nitrogen with high aggregation and the predominance of N3 defects in the PL spectra; (iii) low nitrogen with low aggregation and dominant S1 defects in the PL spectra. The first group is characterized by a green glow (excited 405 nm), the second and third groups are characterized by a blue and yellow glow, respectively. The blue glow of the studied crystals is primarily due to the presence of the N3V center. This defect appears as a result of the aggregation sequence of nitrogen impurities and corresponds to diamonds subjected to the highest temperature annealing (1100-1260°C). Diamonds containing the S1 center are characterized by a low content and aggregation of nitrogen compared to crystals of other groups. Group (i) diamond crystals, whose PL spectra are dominated by the H3 and 490.7 nm systems, have a more intense brown color. Conclusions. The data obtained indicate that annealing at higher temperatures is responsible for the formation of N3V centers in highly aggregated diamonds. The low %B1 aggregation and nitrogen content are associated with the presence of a nitrogen getter (presumably titanium) in the S1 center. An intense brown color appears in the group of diamonds with dominant systems A, H3 and 490.7 nm, which indicates a possible relationship between nitrogen and the corresponding optical absorption.