Enhanced directional emission from quantum dot films by lattice resonances in c-Si metasurfaces

Artificially constructed planar metasurfaces have attracted significant attention in micro-nano photonic devices in recent years due to their unique capabilities in optical field manipulation and subwavelength-scale advantages. To address limitations in light extraction efficiency and polarization-dependent external components in traditional devices, this study proposes integrating crystal silicon (c-Si) nanoparticle arrays (NPAs) with a CdSe quantum dot (QD) emission layer. Through the coupling effects between surface lattice resonance (SLR) and waveguide modes, efficient polarization-state modulation is achieved in the visible spectrum. QD-generated spontaneous emission photons excite Mie resonances in NPAs, where localized electromagnetic fields interact with array diffraction orders to form SLR and quasi-waveguide modes, significantly enhancing fluorescence trapping and secondary radiation efficiency. Adjusting nanoparticle diameter modifies the system's equivalent refractive index, dynamically controlling emission angles and polarization degree. The experiment employed QD-PMMA spin-coating and solution self-assembly processes to prepare 200 nm and 13 nm thick QD films. Angle-resolved photoluminescence (PL) measurements revealed that increasing nanoparticle diameter to 170 nm enhanced fluorescence intensity by 14× through SLR-induced near-field enhancement, with directional emission occurring at ±6.5° perpendicular to the incident plane. For 200 nm QD films coupled with the NPA, a linear polarization degree of 61% was achieved within ±12° of the normal direction. The synergy between QDs' narrowband emission and the metasurface's polarization selectivity eliminates the need for traditional external polarizers, offering a novel approach for miniaturized planar light sources.