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Important features in the spectral and temporal photoluminescence excitation of single nitrogen-vacancy (NV) centers in diamond are reported at conditions relevant for quantum applications. Bidirectional switching occurs between the neutral (NV^0) and negatively charged (NV^-) states. Luminescence of NV^- is most efficiently triggered at a wavelength of 575 nm which ensures optimum excitation and recharging of NV^0. The dark state of NV^- is identified as NV^0. A narrow resonance is observed in the excitation spectra at 521 nm, which mediates efficient conversion to NV^0.
Beha et al. (Thu,) studied this question.