Manipulation of Magnetic Dipole Emission from Eu3+ with Mie-Resonant Dielectric Metasurfaces [component]

Mie-resonant high-index dielectric nanoparticles and metasurfaces have been suggested as a viable platform for enhancing both electric and magnetic dipole transitions of fluorescent emitters. While the enhancement of the electric dipole transitions by such dielectric nanoparticles has been demonstrated experimentally, the case of magneticdipole transitions remains largely unexplored. Here, we study the enhancement of spontaneous emission of Eu 3+ ions, featuring both electric and
more » ... and magnetic-dominated dipole transitions, by dielectric metasurfaces composed of Mie-resonant silicon nanocylinders. By coating the metasurfaces with a layer of an Eu 3+ doped polymer, we observe an enhancement of the Eu 3+ emission associated with the electric (at 610 nm) and magneticdominated (at 590 nm) dipole transitions. The enhancement factor depends systematically on the spectral proximity of the atomic transitions to the Mie resonances as well as their multipolar order, which is controlled by the nanocylinder radius. Importantly, the branching ratio of emission via the electric or magnetic transition channel can be modified by carefully designing the metasurface, where the magnetic dipole transition is enhanced more than the electric transition for cylinders with radii of about 130 nm. We confirm our observations by numerical simulations based on the reciprocity principle. Our results open new opportunities for bright nanoscale light sources based on magnetic transitions. In optics, the interaction of matter with the magnetic field of light is usually ignored since it is several orders of magnitude weaker as compared to the interaction of matter with the electric field of light. An important exception, however, is exemplified by trivalent lanthanide ions, such as Eu 3+ and Er 3+ , which are well known to exhibit magnetic-dipole transitions in the visible and near-infrared region, respectively. Trivalent lanthanides have been intensely studied for a few decades and remain an active subject of research. 1-3 Recently, for example, Novotny et al. 2 demonstrated that the magnetic dipole transition of Eu 3+ ions can be selectively excited using azimuthally polarized focused laser beams possessing high magnetic and vanishing electric field at the centre. As such, the engineering of the optical
doi:10.1021/acs.nanolett.8b04268.s002 fatcat:hsdip57oqvhvbmjt2wagvxsqke