Interaction with Silver Nanowires Disrupts the Excitation Pathways in Upconverting Nanoparticles

Despite years of research, detailed understanding of the coupling between metallic and upconverting nanoparticles (UCNPs) remains elusive. Although many studies reported modified upconverted luminescence (UCL) intensity and/or lifetime upon coupling, the driving force behind the change was often vague. Published reports clearly indicate that surface plasmon polaritons (SPPs) can impact each step of the photon upconversion: excitation, energy transfer, relaxation, and emission. For silver nanowires, which do not exhibit a clear, single plasmon resonance, clarification of the role played by SPPs is additionally complex. In this work, we employ studies of hyperspectral mapping and luminescence dynamics combined with finite-difference time-domain simulations to reveal how SPPs in silver nanowires impact the UCL. We present evidence that the interaction with SPPs leads to shortening of the emitting state, not the intermediate state, lifetime. The faster population decay alters the excitation pathways and results in modifications of the UCL spectra. This work shows that interactions with SPPs not only changes the UCL intensity and dynamics but can also be used to tune the spectral properties of UCNPs.