Selective Enhancement of Crystal‐Field‐Split Narrow f‐f Emission Lines of Europium Ions by Electric and Magnetic Purcell Effect of Mie Resonant Silicon Nanosphere

Abstract Narrow‐band Purcell enhancement for electric and magnetic dipole emitters by high‐order Mie resonances up to the magnetic and electric octupole modes of a silicon nanosphere antenna is experimentally demonstrated. Eu³⁺ complexes are attached on the surface of a silicon nanosphere 160 to 316 nm in diameter, and the photoluminescence and scattering properties are investigated. It is shown that the branching ratio of the ⁵D₀→⁷F_j (j = 0–4) f‐f transitions of Eu³⁺ is controlled in a wide range by tuning the resonance wavelength of a silicon nanosphere by the size. Because of the high‐quality factor resonances, not only a specific ⁵D₀→⁷F_j transition, but also a specific Stark sublevel transition whose spectral separation is 3–9 nm can be selectively enhanced by precisely controlling the size of a silicon nanosphere with the accuracy of ≈2 nm.