Comment on “Nickel–nitrogen complexes in synthetic diamond: The 2.427 eV absorption system”

Abstract

The 1.660 eV and 2.427 eV centers are commonly observed in optical spectra from nitrogen- and Ni-rich diamond grown by high-pressure high-temperature technique, followed by annealing for typically 16 h at 1500 °C. They have been previously associated by Kupriyanov et al. with one defect center based on annealing and photoluminescence (PL) excitation results. On the contrary, based on uniaxial stress measurements, Rino et al. recently suggested that those centers originate from different defects. This finding brought them to a conclusion that localized optical absorption via internal transitions at one, low-density defect center (2.427 eV) can produce luminescence from another low-density center (1.660 eV). In this communication, on the basis of polarization-resolved PL measurements the results of Kupriyanov et al. are supported and conclusions of Rino et al. are strongly questioned. The symmetry of the 1.660 eV center is suggested as triclinic or monoclinic-I. Possible reasons for inconsistencies in uniaxial stress results of Rino et al. are discussed.