Energy-Resolved Hot-Carrier Relaxation Dynamics in Monocrystalline Plasmonic Nanoantennas

Hot carriers are energetic photoexcited carriers driving a large range of chemicophysical mechanisms. At the nanoscale, an efficient generation of these carriers is facilitated by illuminating plasmonic antennas. However, the ultrafast relaxation rate severally impedes their deployment in future hot-carrier based devices. In this paper, we report on the picosecond relaxation dynamics of hot carriers in plasmonic monocrystalline gold nanoantennas. The temporal dynamics of the hot carriers is experimentally investigated by interrogating the nonlinear photoluminescence response of the antenna with a spectrally resolved two-pulse correlation configuration. We measure time-dependent nonlinearity orders varying from 1 to 8, which challenge the common interpretation of multiphoton gold luminescence. We demonstrate that the relaxation of the photoexcited carriers depends of their energies relative to the Fermi level. We find a 60% variation in the relaxation rate for electron hole pair energies ranging from ca. 0.2 to 1.8 eV. The quantitative relationship between hot-carrier energy and relaxation dynamics is an important finding for optimizing hot-carrier-assisted processes and shed new light on the intricacy of nonlinear photoluminescence in plasmonic structures.