All‐Optical Electric Field Sensing with Nanodiamond‐Doped Polymer Thin Films

The nitrogen‐vacancy (NV) center is a photoluminescent defect in diamond that exists in different charge states, NV ‐ and NV 0 , that are sensitive to the NV's nanoscale environment. Here, all‐optical voltage sensing with NV centers in fluorescent nanodiamonds (FNDs) is demonstrated in a solid‐state device based on electric field‐induced NV charge state modulation. More than 95% of FNDs integrated into a polymer‐based capacitor device show a transient increase in NV − PL intensity up to 31% within 0.1 ms after application of an external voltage, accompanied by a simultaneous decrease in NV 0 PL. The NV − PL signal increases with increasing electric field from 0 to 619 kV cm −1 . The best electric field sensitivity for a single FND is 18 V cm −1 Hz −½ . The NV charge state photodynamics are investigated on the millisecond timescale. The change in NV PL is found to strongly depend on the rate of photoexcitation. A model is proposed that qualitatively explains the results based on an electric field‐induced redistribution of photoexcited electrons from substitutional nitrogen to NV centers, leading to a transient conversion of NV 0 to NV − centers. These results contribute to the development of FNDs as reliable, all‐optical, nanoscale electric field sensors in solid‐state systems.