ESR and optical evidence for a Ni vacancy center in CVD diamond

Characterization of a series of correlated electron-spin resonance (ESR) and photoluminescence (PL) lines in diamond grown by chemical vapor deposition is reported. The series consists of a Set of structured PL bands in the range 1.8-2.3 eV, and ESR lines due to an S = 1 center with g = 2.0039(1) and D = 35.8(1) mT at 300 K. PL lines are shown to originate from a defect center with the ground state at 2.24 eV below the conduction band, and with several excited states. The whole set of data can be interpreted in terms of a defect containing a neutral interstitial Ni atom at the center of a divacancy.