Plasmonic Light Emission by Inelastic Charge Transport in Ultrathin Zinc Oxide/Metal Heterostructures

Controlling light emission from plasmonic nanojunctions is crucial for developing tunable nanoscale light sources and integrated photonic applications. It requires precise engineering of plasmonic nanocavity electrodes and a detailed understanding of electrically driven light emission. Using scanning tunneling microscopy-induced luminescence (STML), we studied plasmonic light emission from ultrathin ZnO/Ag(111) inside a silver nanocavity. At positive bias, plasmonic luminescence, caused by radiative decay of localized surface plasmons (LSP), is spectrally low-pass filtered by the ZnO layers. The emission of photon energies above the conduction band edge energy (<b><i>E</i></b>_<b>CB</b>) of ZnO is suppressed, while the spectral distribution below <b><i>E</i></b>_<b>CB</b> resembles the LSP resonance on Ag(111). This spectral filtering is absent at negative bias and depends on the local electronic structure, as confirmed by spatial STML mapping. Our findings demonstrate that the ZnO conduction band serves as the initial state for plasmonic luminescence driven by inelastic electron transport across the ZnO/Ag(111) interface.