Phosphorescence and donor-acceptor pair recombination in laboratory-grown diamonds

Abstract

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 (NS0 »BS0), 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 NS- are identified after optical excitation at or above the indirect band gap. NS- is much shallower (∼0.2 eV) than previously thought and plays a key role in resetting the NS0BS0 donor-acceptor pairs.