Luminescence of natural carbon nanomaterial: Impact diamonds from the Popigai crater

• Broad band luminescence is similar to that in ultra-disperse diamonds and CVD films.
• Fine structure is due to N, Cr, and Ni impurities and structural defects.
• Nitrogen impurity may be aggregated to NV, H3 and N3 defects.
• Luminescence decay is a sum of two exponents with short lifetime in the 5 to 9 ns range.

Impact diamonds (IDs) from the Popigai crater are aggregates of nanoparticulate graphite and cubic and hexagonal diamonds. IDs demonstrate broad-band emissions at 3.05, 2.8, 2.3 and 2.0 eV, which are associated with structural defects and are similar to those in detonation ultra-dispersed diamonds and CVD diamond films. A doublet with components at 1.7856 and 1.7892 eV in some ID samples is related to R1,2 lines of Cr3 + ions in corundum inclusions. The presence of N3, H3, NV0 and NV− vibronic systems in some of the ID samples shows that (i) there is nitrogen impurity and (ii) samples underwent high temperature annealing that promoted vacancies and nitrogen diffusion and defect aggregation. The luminescence decay fits with a sum of two exponential components: lifetime of the fast one is in the 5 to 9 ns range. Parameters of the traps responsible for broad thermoluminescence peaks at 148, 180, 276 and 383 K were estimated.

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