Fig. show the fluorescence (FL) spectra from the bulk diamond, the 156 nm and the 48 nm NDs. Each NV charge state is characterized by its characteristic fluorescence spectrum, with zero-phonon lines (ZPL) at 575 nm and 638 nm for the NV 0 and NV -, respectively. In addition, a phonon sideband, peaked around 620 nm for the NV 0 and 700 nm for the NV -, is observed, extending up to ≈850 nm in both cases. On average, the two NDs samples presented a lower overall FL than bulk diamond (not apparent in figure , where the spectra are normalized to the NV -ZPL for comparison). Moreover, NDs showed a larger component from the NV 0 s with respect to the bulk diamond (represented as black and light red curves, respectively). This is consistent with the idea that surface effects favor the NV 0 centers, thus affecting the relative concentration of the different charge states.