Electron paramagnetic resonance studies of the neutral nitrogen vacancy in diamond

Abstract

Despite the numerous experimental and theoretical studies on the negatively charged nitrogen vacancy center $({\mathrm{NV}}^{\ensuremath{-}})$ in diamond and the predictions that the neutral nitrogen vacancy center $({\mathrm{NV}}^{0})$ should have an $S=\frac{1}{2}$ ground state, ${\mathrm{NV}}^{0}$ has not previously been detected by electron paramagnetic resonance (EPR). We report new EPR data on a trigonal nitrogen-containing defect in diamond with an $S=\frac{3}{2}$ excited state populated via optical excitation. Analysis of the spin Hamiltonian parameters and the wavelength dependence of the optical excitation leads to assignment of this $S=\frac{3}{2}$ state to the $^{4}A_{2}$ excited state of ${\mathrm{NV}}^{0}$. This identification, together with an examination of the electronic structure of the NV centers in diamond, provides a plausible explanation for the lack of observation (to date) of an EPR signal from the ${\mathrm{NV}}^{0}$ ground state.