Visible-light excited red-emitting vacancies at carbon interstitials as indicators of irradiated and annealed Type Ia diamonds

During the last decades many studies have been carried out to investigate how point defects and aggregates respond and evolve in natural Type Ia diamonds as a result of treatments, and a number of underlying mechanisms have been identified and interpreted. However, the analysis of radiation-induced creation/ionization of defects, as well as their migration and aggregation in secondary defect structures, often requires experimental approaches which can hardly constitute a simple-to-use diagnostic tool for the identification of artificially treated diamonds. Here we disclose a novel simple indicator of artificial exposure of Type Ia diamonds to ionizing radiations and subsequent annealing. This indicator consists in narrow photoluminescence lines in the red region, between 681 and 725 nm, we recently found to result from vacancies trapped by interstitial carbon aggregates and platelets. Our results demonstrate that interstitial structures become sites of vacancy trapping – by thermal migration of radiation-induced vacancies – only when diamond undergoes treatments. We give the rigorous validation of the new spectroscopic probe of artificial treatments analysing photoluminescence and infrared absorption spectra of well-known H1b and H1c centres in a hundred samples. Importantly, the method is based on emission lines which do not require neither high photon-energy excitation nor cryogenic temperatures.