High-density nitrogen-vacancy (NV) ensembles, containing a large number of quantum sensors, offer great potential for enhancing the performance of quantum magnetometry. However, the high concentration of nitrogen defects in diamond introduces abundant charge donors and leads to substantial charge-state fluctuations, which impose a fundamental limitation on practical performance. In this study, we observe recharging-induced spin depolarization and spontaneous repolarization in an electron-rich NV ensemble by systematically varying the dark interval between laser and microwave pulses. Different initialization conditions influence the observed dynamics. By concurrently tracking both charge and spin dynamics, we identify long-range defect-mediated electron transport as the dominant mechanism underlying charge conversion and the associated spin-state degradation. Our findings provide insights into electron-transport dynamics in deep-level defects in diamond, and offer practical guidelines for stabilizing the ${\mathrm{NV}}^{-}$ charge state and manipulating spin polarization.

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• Charge migration
• Coherent control
• Quantum control
• Quantum sensing
• Single- and few-photon ionization & excitation
• Nitrogen vacancy centers in diamond