Fig. 1: Illustration of the experimental configuration. An aluminum nanodisk serves as a plasmonic nano-antenna and is fabricated at the end of an NSOM fibered tip.

This tip is glued to a tuning fork, and via a feedback loop mechanism, the position of the antenna can be deterministically controlled within a few nanometers from the sample, ensuring precise manipulation in all three spatial dimensions. The plasmonic nano-antenna is excited by a supercontinuum laser, filtered using a series of interference filters to isolate a specific wavelength range with a 2 nm bandwidth. The laser beam, rendered linearly polarized, is injected into the optical fiber supporting the tip and antenna, resulting in the optical excitation of the latter. The localized plasmonic fields generated by the antenna are used to excite Y₂O₃: Eu³⁺ nanoparticles, which are deposited on a glass substrate. SEM images of an antenna and of a nanoparticle are shown. Luminescence emitted by the nanoparticle is collected using an immersion objective (×100, NA = 1.3) from the substrate side and measured with a spectrometer. The inset provides the emission spectrum of europium ions in the Y₂O₃ matrix, along with the partial band diagram of these emitters. It is important to note that, at the wavelengths under consideration, electric and magnetic dipole transitions dominate the optical response of europium ions, with higher-order processes, such as electric quadrupole transitions, being negligible⁵¹