A Gentle Push for a Giant Leap: Harnessing Guided-Mode Leakage to Control Bound States in the Continuum-Coupled Quantum Dot Emission

Fluorescence enhancement lies at the heart of many optical biosensing and diagnostic technologies, yet most photonic approaches still rely on intrinsically bright emitters or fabrication-intensive nanoresonators. Here, we introduce an unconventional strategy that turns a nominally "weak" photonic mode into a powerful resource. Through simple, frugal interface engineering, we show that leaky guided-mode resonances (GMRs), often regarded as optical loss channels, can be harnessed to amplify the excitation of two orthogonally polarized bound states in the continuum (BICs) within a one-dimensional photonic crystal. This synergistic interaction enables deterministic control of quantum dot (QD) photoluminescence, yielding wavelength-specific emission enhancement up to 691× for semiconductor QDs and 206× for biomass-derived carbon QDs, while achieving degrees of polarization up to 96% and angular divergences as small as 1.3°. Angle-resolved spectroscopy and back-focal-plane imaging, corroborated by time-resolved fluorescence decay analysis, reveal the mechanistic interplay between GMR-assisted excitation and BIC-mediated radiative extraction. By reimagining leaky modes as excitation amplifiers rather than parasitic losses, this work establishes a physically transparent, sustainable, and scalable route to polarization-encoded on-chip light sources and fluorescence-based diagnostic technologies.