Specifics of high-temperature annealing of brown CVD single crystal diamonds at graphite-stable and diamond-stable conditions

Changes in the set and concentration of optically active defects in brown single-crystal CVD diamonds under high-temperature annealing at low pressure (LPHT) and high pressure (HPHT) were studied by optical spectroscopy. It is established that the pink tint in diamond color, which appears after LPHT annealing and disappears after HPHT annealing, is caused by NV centers. Transformation of nitrogen-vacancy centers observed in the course of annealing follows the NV -> NVN -> N3V pattern and is accompanied by a color change from dark brown to practically colorless. At the same time, the absorption spectrum takes the form typical of the IIa + Ib type diamonds with nitrogen concentration at the level of 1-2 ppm. The broadband luminescence present in all CVD diamonds studied is tentatively associated with some extended defects that do not disappear even during HPHT annealing. The set of charge carriers traps is sensitive to annealing parameters, and the high-temperature peak near 661 K appearing after the LPHT annealing on thermoluminescence is considered as promising for dosimetry of ionizing and UV radiations.