Enhancing Magnetic Dipole Emission from 2D Hybrid Organic-Inorganic Perovskites via Mie Resonator Dimers.

Recently, layered 2D hybrid organic-inorganic perovskites (HOIPs) like butylammonium lead iodide (BAPbI) have been shown to exhibit ultrabright out-of-plane-oriented magnetic dipole (MD) photoluminescence (PL) arising from self-trapped excitons (STEs). The MD emission, however, has considerable spectral overlap with the dominant in-plane-oriented electric dipole (ED) transitions, making it difficult to interrogate STE properties. Here, we theoretically investigate opportunities to use Mie resonator dimers to selectively enhance the MD emission through the Purcell effect. We calculate relative MD and ED Purcell enhancements at dimer center as well as average values across the dimer geometry. We show that the selective enhancement is excellent at the dimer center enabling nearly pure MD emission (96%) at the MD emission peak (540 nm) as well as predominant MD emission (up to 77%) across the entire integrated spectrum (500-600 nm). We subsequently show, however, that away from the dimer center, Purcell enhancement of the relatively weak out-of-plane ED transitions competes with MD enhancements, reducing the branching ratio (73% at the MD emission peak, 39% spectrally integrated). Lastly, we calculate how the Mie resonator dimer modifies the PL spectra and emitter radiation pattern. Notably, for volume-averaged dipoles, both MD and ED emissions are mediated via the dimer, producing a single donut-beam-like radiation pattern across the entire emission spectrum. Our results clarify the potential for achieving "pure" MD emission from 2D HOIPs via simple Mie resonator Purcell enhancements and highlight the importance of designing nanophotonic structures that can maintain desired selective enhancements away from high-symmetry points.