Stacked nanogap plasmons for multispectral photoluminescence

Plasmonic metasurfaces supporting multiple resonances are highly desirable for enhancing optical fields at distinct wavelengths. Here, we demonstrate doubly stacked nanogap arrays that exhibit dual Fabry-Pérot resonances of the gap plasmons. Numerical simulations reveal that both resonances appear at different wavelengths due to the lateral length difference between the upper and lower nanogaps. Furthermore, we fabricated stacked nanogap arrays by alternating metal-insulator deposition, electron beam (e-beam) lithography, and ion milling. Due to the dual plasmon resonance, the photoluminescence spectra of spin-coated dyes (R6G and IR-820) show distinct modifications near the two reflection dips. These results highlight stacked nanogaps as a promising platform for co-localized multicolor dye excitation and multispectral photoluminescence engineering, with potential applications in multi-wavelength light sources and multicolor displays.