Spectroscopic study of cobalt‐related optical centers in synthetic diamond

This article presents evidence that cobalt forms a series of optically active defect centers in diamond grown by high‐temperature, high‐pressure synthesis. Photoluminescence (PL) studies reveal that the newly observed vibronic systems with zero‐phonon energies at 1.989, 2.135, 2.207, 2.277, 2.367, and 2.590 eV appear only in samples grown using a cobalt‐containing solvent–catalyst. Results of an annealing study, carried out in the temperature range 1500 to 1800 °C, establish that many of the new bands appear during the temperature regime of nitrogen aggregation. It is therefore proposed that nitrogen forms complexes with cobalt to produce optically active centers, in a manner analogous to that of nickel point defects in diamond. Detailed radiative decay time measurements and temperature dependence measurements show that all but one of the bands which are here associated with nitrogen–cobalt complexes have long radiative decay times (∼100 μs), and this again is a characteristic of the PL centers arising fr...