Optimum photoluminescence excitation and recharging cycle of single nitrogen-vacancy centers in ultrapure diamond

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 (NV0) and negatively charged (NV ^-) states. Luminescence of NV ^- is most efficiently triggered at a wavelength of 575nm which ensures optimum excitation and recharging of NV0. The dark state of NV ^- is identified as NV0. A narrow resonance is observed in the excitation spectra at 521nm, which mediates efficient conversion to NV0.