Single-Particle Emission Spectroscopy Resolves d-Hole Relaxation in Copper Nanocubes

Resolving the dynamics of photoexcited d-holes in metallic nanostructures is one step in the rational design of plasmonic photocatalysis. Here, we track the creation and relaxation of charge carriers in catalytically important plasmonic copper nanocubes using single-particle spectroscopy. We show that interband transitions dominate the absorption and emission of 60–160 nm copper nanocubes, and in contrast to gold nanorods, the LSPR is less important to the emission. We uncover the plasmonic enhancement of emission hidden in ensemble measurements by resolving the size-dependent line shape and quantum yield. Quantum yield analysis reveals the energy dependence of d-hole lifetimes. We demonstrate that the effect of excitation energy on quantum yield is stronger in copper nanocubes than in gold nanocubes of equivalent size due to differences in the band structure and the probabilities of hole scattering. Finally, we establish that emission spectroscopy is useful to understand the physical chemistry of d-holes in plasmonic photocatalysts.