Enhanced photoluminescence at the edges of light-emitting metasurfaces induced by guided modes

Driven by the continuous advancement in solid-state lighting, medical imaging, display anti-counterfeiting technologies, and wireless optical communication, there is a growing demand for efficient energy down-conversion devices. Limited by low light absorption and emission efficiency, existing energy down-conversion devices suffer from low effective input energy, resulting in low conversion efficiency. However, using metasurfaces enhances the interaction between light and matter, significantly improving the out-coupling efficiency of energy down-conversion devices. This report's experiments discovered a notable phenomenon of edge, significant photoluminescence enhancement (PLE) at the edges of crystal silicon (c-Si) nanoparticle array (NPA) coated with a 530 nm thick film of dye molecules when illuminated with ultraviolet (UV)-extended light. This phenomenon disappears when the thickness of the dye film is reduced to 100 nm. Analysis reveals that the effective refractive index of the polymer layer encapsulating the particle array is higher than that of the substrate and air, forming the waveguide layer due to refractive index matching. The dye molecules induce Mie multipole resonances in the particles upon spontaneous emission, coupling with the periodic array's waveguide modes to form quasi-guided modes, resulting in strong scattering into free space. Furthermore, when the sample is excited with a laser close to the particle array, significant scattering is observed at the edges, with the PL intensity of the edge linearly decreasing as the laser moves away, further confirming the source of PL intensity of the edge as originating from the planar waveguide modes.