Synergistic Chiral and Magnetic Enhancement of Circularly Polarized Luminescence in a Vortexed Plasmonic Nanocavity.

Abstract

Lanthanide complexes exhibit promising circularly polarized luminescence (CPL) due to sharp emissions, large dissymmetry factors, and high photostability from <i>f</i>-<i>f</i> transitions. However, practical applications are limited by low quantum yields (QYs) and an insufficient solid-state brightness. While conventional plasmonic nanostructures excel at electric dipole enhancement, they are less effective for lanthanide luminescence since <i>f</i>-<i>f</i> transitions are predominantly magnetic dipole-allowed. We address this limitation by using nanocube-on-mirror (NCoM) plasmonic resonators coupled to chiral Eu³⁺/organic complexes for magnetic field enhancement. The luminescence dissymmetry factor (<i>g</i>_lum) increases from 0.06 to 0.6, compared to only 2-fold enhancement with nanoparticle-on-mirror structures. Vortex-nanocube-on-mirror (VCoM) structures generating superchiral fields further enhance both electric and magnetic dipole transitions, achieving <i>g</i>_lum up to 0.75 with QY up to 0.57. This CPL enhancement strategy has also been successfully applied to Tb³⁺/organic complexes, which showcases potential anticounterfeiting applications. This work establishes magnetic field enhancement as an effective strategy for advancing chiroptic applications, representing one of the highest CPL enhancements for lanthanide complexes and enabling next-generation chiral photonic devices.