Giant Magnetic Purcell Effect Induced by High-Order Mie Resonances.

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 TiO2 spheres to selectively enhance magnetic dipole emission from Eu3+ 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 TiO2 enables near-field Purcell enhancement to be converted into observable far-field radiation. We further develop a surface-grafting strategy that positions Eu3+ 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 Eu3+ 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.