Styles, R.Han, M.Goris, T.Partridge, J.G.Johnson, B.C.Rosal, B.D.Abraham, A.N.Ebendorff-Heidepriem, H.Gibson, B.C.Dontschuk, N.Tetienne, J.P.Reineck, P.2025-10-142025-10-142025Advanced Functional Materials, 2025; e12068-1-e12068-91616-301X1616-3028https://hdl.handle.net/2440/147784OnlinePubl. Available online 24 July 2025The nitrogen-vacancy (NV) center is a photoluminescent defect in diamond that exists in different charge states, NV- and NV⁰, 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 NV⁰ 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 NV⁰ to NV⁻ centers. These results contribute to the development of FNDs as reliable, all-optical, nanoscale electric field sensors in solid-state systems.en© 2025 The Author(s). Advanced Functional Materials published by Wiley-VCH GmbH. This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made.charge state sensing; nanodiamond; nitrogen-vacancy center; polymer thin-film; voltage sensingJournal article10.1002/adfm.202512068746709Han, M. [0000-0003-3742-1223]Ebendorff-Heidepriem, H. [0000-0002-4877-7770]