Electron paramagnetic resonance and photochromism of N₃V⁰ in diamond

The defect in diamond formed by a vacancy surrounded by three nearest-neighbor nitrogen atoms and one carbon atom, [Formula: see text], is found in the vast majority of natural diamonds. Despite [Formula: see text] being the earliest electron paramagnetic resonance spectrum observed in diamond, to date no satisfactory simulation of the spectrum for an arbitrary magnetic field direction has been produced due to its complexity. In this work, [Formula: see text] is identified in [Formula: see text]-doped synthetic diamond following irradiation and annealing. The [Formula: see text] spin Hamiltonian parameters are directly determined and used to refine the parameters for [Formula: see text], enabling the latter to be accurately simulated and fitted for an arbitrary magnetic field direction. Study of [Formula: see text] under excitation with green light indicates charge transfer between [Formula: see text] and [Formula: see text]. It is argued that this charge transfer is facilitated by direct ionization of [Formula: see text], an as-yet unobserved charge state of [Formula: see text].