Photoluminescence studies of the 523.7 nm optical centre in HPHT synthetic diamond

The 523.7nm centre is very commonly observed in electron irradiated HPHT synthetic diamond, but not in CVD samples with high N content up to 50ppm. Absorption studies indicated that the 523.7nm centre was caused by nitrogen-interstitials complexes, and this hypothesis was supported by the insensitivity of its zero phonon line to stress. However, its high annealing temperature, strong broad phonon sideband and lack of high energy local vibrational modes suggest that the 523.7nm centre was more probably vacancy-related.