Vertical Emission of Blue Light from a Symmetry Breaking Plasmonic Nanocavity‐Emitter System Supporting Bound States in the Continuum

A σ h symmetry‐breaking plasmonic honeycomb nanocavities (PHC) is proposed and realized that support quasi‐BIC resonance modes with high‐Q factors. The anodic oxidation‐engineered strategy breaks out‐of‐plane symmetry while preserving in‐plane symmetry, enabling the PHC to exhibit collective plasmonic lattice resonances (PLR) couplings and achieve Q‐factors exceeding 10 6 . Experimentally, perovskite quantum dots (PQDs) are coupled to the PHC, demonstrating effective tuning of their emission properties and beam quality in the blue spectral region, achieving a 32‐fold emission enhancement by suppress Ohmic loss and the life time of quantum emitters, simultaneously realize vertical emission in the 2.556 – 2.638 eV region, with a far‐field hexagonal beam shape and a full width at half maximum of 12.6 degree under optimal coupling conditions. Furthermore, topological band inversion is demonstrated and characterized by Zak phase transitions by continuously tuning the system parameters, confirming that the PHC supports topologically non‐trivial q‐BIC due to PLR coupling. The PHC presents itself as a promising next‐generation, high‐brightness nanoscale light source matrix, which can be directly scaled up to cover a wide wavelength range from UV to IR.