Nitrogen-vacancy (NV) centers in nanodiamonds are promising platforms for nanoscale quantum sensing in biological and condensed-matter environments, but their performance is often limited by charge-state instability and strain-induced spectral fluctuations. Using spin-state-dependent emission measurements, we demonstrate that controlled optical excitation can stabilize the local charge environment surrounding the NV centers in nanodiamonds, thereby improving sensing stability. We observe that spin-state-dependent spectral emission linewidth and splitting saturate as a function of excitation laser power density, which correlates with a reduction in charge fluctuations across nanodiamonds with varied sizes and impurity concentrations. To elucidate these measurements, we develop a macroscopic theoretical model that reproduces the ensemble-averaged response of large NV populations without requiring explicit simulation of microscopic charge dynamics. Furthermore, we introduce incoherent sensing protocols that exploit environmental noise to achieve sensitivity of $\mu \text{T}/\sqrt{\text{Hz}}$, even in regimes of strong spin decoherence. These results provide a practical route to enhancing the robustness of NV-based quantum sensors and an optically addressable platform for physically unclonable imaging tags relevant to quantum security and anticounterfeiting applications.

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• NV centers
• Quantum engineering
• Quantum metrology
• Quantum optics
• Quantum sensing
• Diamond