Excited states of the negatively charged nitrogen-vacancy color center in diamond

Excited states of the negatively charged nitrogen-vacancy color center in diamond are studied using ab initio many-body perturbation theory (within GW approximation and Bethe-Salpeter equation), including electronic exchange, correlation, and electron-hole interaction effects. We find that three singlets, one of which exhibits an intersystem crossing with the excited triplet, may be relevant for the fluorescence process in a way which has never been considered before. The calculated zero-phonon line for the visible excitation and that for the transition among the singlets are in good agreement with the experiments.