Friedrich‐Wintgen Bound States in the Continuum in Hybrid Plasmonic‐Dielectric Structures for Visible Light Emission

High quality factor (Q‐factor) optical resonances in photonic crystals in the visible range are considered as a powerful tool for advanced sensors, lasers, modulators, and quantum optics. In many practical applications resonances away from the Γ point of the Brillouin zone are essential, as they provide intrinsic angular selectivity and momentum control of light. However, these modes are inherently more radiative, and this limitation becomes particularly severe in hybrid or plasmonic systems, where metal‐induced absorption and scattering losses further suppress the achievement of high‐Q resonances at off‐Γ point. Here we demonstrate that in a hybrid plasmonic‐dielectric periodic metasurfaces with a broken symmetry, the strongly coupled interfering resonances maintain the Friedrich‐Wintgen bound states in the continuum (FW‐BICs), resulting in record‐high values of the leaky mode Q‐factors among the off‐Г‐point BIC type of modes in the visible range. The hybrid design consists of an Al 2 O 3 photonic crystal slab on a corrugated aluminum substrate with a period of 400 nm, covered with a thin layer of CdSe/CdZnS colloidal nanoplatelets as the light‐emitting material. The white‐light reflection and photoluminescence spectra measurements reveal FW‐BIC states with a Q‐factor reaching 709 around wavelength 605 nm, which is in good agreement with our numerical full‐wave simulations.