Fig. 1. (a) Photograph showing the electrospray deposition of FNDs on an ITO-coated glass substrate mounted in a lens tube. The white arrow denotes the spray. (b) Photograph of a FND/ITO-coated glass substrate, prepared with a deposition time of 25 min. (c) Photograph of an FND/ITO-coated glass substrate in a synchrotron radiation beam path. The external white light was turned on to show the position of the substrate, which was mounted on a vacuum-compatible translation stage. (d) Photograph of an FND/ITO-coated glass substrate irradiated by a synchrotron radiation beam of 50 nm in wavelength. With a beam flux of 1.1 × 10¹² photons per s, the red fluorescence from NV⁰ centers hosted in FNDs could be readily seen with the naked eye in reflective mode when the external light was turned off. The red arrow in (c) denotes the FND film of ∼10 mm diameter, and the white arrow in (d) indicates the beam position, i.e., the red fluorescence spot with a size of about 3 × 3 mm².