Coupling between dual resonance modes of plasmonic nanorod arrays and emission of R6G in plasmon resonance energy transfer

Plasmon resonance energy transfer (PRET) enhances energy transfer between plasmonic nanostructures and fluorophores by exploiting spectral overlap, thereby strengthening the light-matter interactions. However, conventional PRET systems rely on single-mode coupling, which limits their tunability and applicability to fluorophores with broad or multipeak emission spectra. Here, we introduce a dual-mode PRET system consisting of silver nanorod arrays coupled with Rhodamine 6G (R6G) molecules embedded in a PMMA matrix. By tuning the nanorod length, we achieved the simultaneous coupling of two longitudinal plasmonic resonance modes with the R6G emission band. Importantly, a strong emission peak results from the enhanced excitation and emission rates of R6G molecules caused by the well-spectral overlap between the plasmonic resonance modes of the silver nanorods and the R6G emission band, reducing the fluorescence lifetime to 0.43 ns. In contrast, weak spectral overlap produces a lower emission intensity and a longer fluorescence lifetime of 2.1 ns. The proposed PRET system can offer a tunable dual-mode platform with promising potential for next-generation biosensing, fluorescence modulation, and photonic-device applications.