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 (${\mathrm{NV}}^0$) and negatively charged (${\mathrm{NV}}^{-}$) states. Luminescence of ${\mathrm{NV}}^{-}$ is most efficiently triggered at a wavelength of 575 nm which ensures optimum excitation and recharging of ${\mathrm{NV}}^0$. The dark state of ${\mathrm{NV}}^{-}$ is identified as ${\mathrm{NV}}^0$. A narrow resonance is observed in the excitation spectra at 521 nm, which mediates efficient conversion to ${\mathrm{NV}}^0$.

Figure 1

Spectral and temporal analysis of the PL emission from an individual nitrogen-vacancy center at a temperature of $T=10\mathrm{K}$. PL spectra are measured under excitation at a wavelength of (a) 521 and (b) 550 nm. The second-order photon correlation function $g^{(2)}(\tau )$ is shown in the inset of (a). The temporal PL decay for ${\mathrm{NV}}^0$ and ${\mathrm{NV}}^{-}$ is depicted in the inset of (b).

Figure 2

PLE spectra of ${\mathrm{NV}}^{-}$ (red circles), ${\mathrm{NV}}^{-}$ with an additional repump laser at 488 nm (black squares), and ${\mathrm{NV}}^0$ (blue triangles) of an individual center at $T=10\mathrm{K}$. The inset compares PLE spectra of single ${\mathrm{NV}}^{-}$ at $T=300\mathrm{K}$ (gray) and $T=10\mathrm{K}$ (red). In all traces filled and open symbols correspond to ZPL and rescaled PSB intensities, respectively.

Figure 3

(a) Schematic representation of the low-temperature absorption spectra of ${\mathrm{NV}}^{-}$ (red) and ${\mathrm{NV}}^0$ (blue) together with relevant switching cycles (top). Red crosses denote breaks in the recharging cascade. The gray shaded region (ii) corresponds to the joint absorption of both charge states, where continuous charge switching (stars denote excited states) and therefore efficient NV luminescence is possible. (b) Simplified electronic energy schemes of the nitrogen-vacancy center. The optical transition from ground state (GS) to excited state (ES) is followed either by an excitation of an electron ($e^{-}$) into the conduction band (green arrows) for ${\mathrm{NV}}^{-}$ (right) or an excitation of a hole ($h^{+}$) into the valence band (orange arrows) for ${\mathrm{NV}}^0$ (left). An additional electronic resonance of ${\mathrm{NV}}^{-}$ is located in the conduction band of diamond.