Giant Magnetic Purcell Effect Induced by High‐Order Mie Resonances

ABSTRACT

The Purcell effect provides an effective route for tailoring light–matter interactions. However, efficient enhancement of magnetic dipole transitions remains challenging because magnetic light–matter coupling is intrinsically weak and strongly outcompeted by dominant electric dipole channels. Here we exploit high‐order Mie resonances supported by low‐loss TiO ₂ spheres to selectively enhance magnetic dipole emission from Eu ³⁺ emitters. Numerical analysis shows that the coupling between a point emitter and Mie resonance increases with the resonance order, while the low optical loss of TiO ₂ enables near‐field Purcell enhancement to be converted into observable far‐field radiation. We further develop a surface‐grafting strategy that positions Eu ³⁺ emitters within ∼2 nm of the sphere surface to maximize emitter–resonator coupling. Using single‐particle spectroscopy and a magnetic 32‐pole Mie resonance, we achieve a ∼8.7‐fold enhancement of the magnetic dipole transition branching ratio of Eu ³⁺ ions, accompanied by an ∼38.1‐fold increase in the magnetic dipole decay rate. Our findings not only extend Mie‐tronics as a promising platform for manipulating light generation but also provide a versatile strategy for magnetic‐field‐driven nanophotonic functionalities.