An undocumented photoluminescence center at 1.789eV was characterized in diamonds which had been grown by using a high-pressure high-temperature technique. It could be observed only in N-free crystals grown in a Fe-containing chamber. The center was unique to diamond, due to its room-temperature linewidth; which could be as narrow as 0.001eV. Polarization, temperature and time-resolved measurements revealed that the corresponding defect had trigonal symmetry, an 0.0037eV splitting in the ground state, vibronic modes of 0.030 and 0.048eV, very weak electron-phonon coupling and a lifetime of 7ms at room temperature. The center was attributed to an interstitial Fe-related defect.

Evidence for a Fe-Related Defect Centre in Diamond. K.Iakoubovskii, G.J.Adriaenssens: Journal of Physics - Condensed Matter, 2002, 14[4], L95-8