Self-Interfering Magnetic Dipole Transition Emission in Rare-Earth Ions Doped Nanoparticles Modulated by Plasmonic Mirror Nanocavity.

In conventional photonics, light-matter interactions are predominantly governed by electric dipole (ED) transition. Although magnetic dipole (MD) transition emission is challenging to detect due to its intrinsic properties, it exhibited significant application potential in biological probes and quantum technologies. Eu3+ ions are considered an ideal system for investigating MD-ED transition emissions owing to their unique energy-level structure as sensitive nanoscale probes for electromagnetic fields. In this paper, a mirror plasmonic nanocavity combining Au nanospheres (NSs) with an Au flake is applied to modulate both ED and MD emissions from Eu3+-doped NaYF4 nanoparticles (NPs). The structure of the mirror nanocavity is systematically adjusted and precisely controlled through the nanoscale manipulation capability of atomic force microscopy (AFM). The emission of MD transition is enhanced as 3-fold on Au flake through the construction of a monolayer Eu3+ ions doped NPs only by self-interference effect. By coupled Au NSs and flake, the intensity of ED transition emissions was restored to 481 times its original magnitude through the utilization of localized surface plasmon resonance (LSPR) effects. A significant enhancement of Eu3+ ions luminescence and artificial modulation of emission ratios are achieved. This tunable platform benefits for detection and manipulation of light-matter interactions at nanoscale.