Nitrogen‐Vacancy Emission from Nanodiamond: Size, Depth, and Surroundings

ABSTRACT The negatively charged nitrogen‐vacancy (NV) center in diamond is a leading solid‐state quantum emitter, offering spin‐photon interfaces over a wide temperature range with applications from electromagnetic sensing to bioimaging. While NV centers in bulk diamond are well understood, embedding them in nanodiamond (ND) introduces complexities from size, NV location, and NV polarizations. NVs in ND show altered fluorescence properties, including longer lifetimes, lower quantum efficiency, and higher sensitivity to dielectric surroundings, which arise from radiative suppression, surface‐induced non‐radiative decay, and escape inefficiency at the diamond‐background interface. Prior models typically addressed isolated aspects, such as dielectric contrast or surface quenching, without integrating full quantum‐optical NV behavior with classical electrodynamics. We present a hybrid framework coupling rigorous electromagnetic simulations with a quantum‐optical NV model including phonon sideband dynamics. NV emission is found to depend strongly on ND size, NV position, and surrounding refractive index. Our results explain observations such as shallow NVs in water‐coated ND appearing brighter than deeper ones in air. This integrated model provides a unified framework for realistic NV in ND emission scenarios and informs the design of efficient NV‐based sensors and quantum devices, advancing understanding of quantum emitter photophysics in nanoscale crystals.