Occurrence of the Si–V defect center in natural colorless gem diamonds

Abstract

The Si–V defect center in diamond (737 nm; 1.682 eV) was long thought to occur only in chemical vapor deposition (CVD)-grown or Si-doped HPHT-grown synthetic diamonds. We report, for the first time, the occurrence of the Si–V defect in ten gem-quality colorless natural diamonds. Many of these samples, including type IIa and Ia diamonds, contained included crystals of olivine (Fo 93–95) and garnet (Ca–Mg-rich), proving their natural origin. The 737 nm photoluminescence feature (actually a doublet at 736.5 and 736.9 nm at 77 K) occurred in association with several additional and previously unreported peaks at 524.4, 550.4, 554.3, 557.9, 558.2, 573.5, 593.3, 594.8, and 714.7 nm, as well as two series of peaks in the ranges 535–539 and 644–652 nm. The intensities of the associated peaks were proportional to the 737 features, suggesting their association with Si as well. Based on olivine (Fo 0.93–0.95) and garnet inclusion (Ca, Mg-rich) chemistry, these diamonds are peridotitic in nature, likely having formed in the upper mantle. The source of the Si remains unclear. Care must be taken to avoid confusion between these natural Si–V diamonds and CVD synthetic diamonds with Si–V features. Fortunately, many of the commonly reported CVD identification features are absent from natural Si–V diamonds, facilitating the separation.