Intense “blue-green” phosphorescence is commonly observed in near-colorless laboratory-grown high-pressure high-temperature diamonds following optical excitation at or above the indirect band gap. We have employed a holistic combination of optically excited time-resolved techniques (in addition to standard spectroscopic characterization techniques) to study the physics of this long-lived phosphorescence and understand luminescence-related charge-transfer processes. It is shown that the properties of the broad “blue-green” luminescence and phosphorescence band can be fully explained by emission from neutral substitutional nitrogen-boron donor-acceptor pairs (${\text{N}}_{\text{S}}^0\cdots {\text{B}}_{\text{S}}^0$), once the configurational change between charge states is considered, and both tunneling between defects and thermal ionization of donors and acceptors is considered. Significant concentrations of metastable ${\text{N}}_{\text{S}}^{-}$ are identified after optical excitation at or above the indirect band gap. ${\text{N}}_{\text{S}}^{-}$ is much shallower ($\sim 0.2$ eV) than previously thought and plays a key role in resetting the ${\text{N}}_{\text{S}}^0\cdots {\text{B}}_{\text{S}}^0$ donor-acceptor pairs.

• Received 2 June 2023
• Accepted 15 September 2023

DOI:https://doi.org/10.1103/PhysRevB.108.165203

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Published by the American Physical Society