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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 (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).