Charge and Spin Dynamics and Destabilization of Shallow Nitrogen-Vacancy Centers under UV and Blue Excitation

Shallow nitrogen-vacancy (NV) centers in diamond offer unique opportunities for studying photochemical reactions at the single-molecule level, such as the photogeneration of radical pairs in proximal molecules. A prerequesite for such experimental schemes is the detailed understanding of the charge and spin dynamics of NV centers exposed to the short-wavelength light required for photoexciting chemical species. Here, we measure and analyze the charge and spin dynamics of shallow NV centers under 445 nm (blue) and 375 nm (UV) illumination. With blue excitation, we observe a power-dependent charge-state preparation accompanied by modest preservation of spin initialization fidelity. Under UV excitation, we find a power-independent charge-state preparation and no spin polarization. We further observe an irreversible aging of NV centers under prolonged exposure to UV, and to a lesser extent, blue laser excitation, which we attribute to formation of new electronic trap states. This aging manifests itself in a reduced charge stability and spin contrast, and is detrimental to the NV sensing performance. We evaluate the prospects and limitations of NV centers for probing photogenerated radical pairs based on experimentally measured sensitivities following blue and UV excitation, and outline the design rules for possible sensing schemes.