Lighting up metal nanoclusters by the H₂O-dictated electron relaxation dynamics

The modulation of traps has found attractive attention to optimize the performance of luminescent materials, while the understanding of trap-involved photoluminescence management of metal nanoclusters greatly lags behind, thus extensively impeding their increasing acceptance as the promising chromophores. Here, we report an efficient passivation of the structural oxygen vacancies in AuAg nanoclusters by leveraging the H₂O molecules, achieving a sensitive color tuning from 536 to 480 nm and remarkably boosting photoluminescence quantum yield from 5.3% (trap-state emission) to 91.6% (native-state emission). In detail, favored electron transfer relevant to the structural oxygen vacancies of AuAg nanoclusters contributes to the weak trap-state emission, which is capable of being restrained by the H₂O molecules by taking Au-O and Ag-O bonds. This scenario allows the dominated native-state emission with a faster radiative rate. In parallel, the H₂O molecules can rigidify the landscape of AuAg nanoclusters leveraging on the hydrogen bonding, thus enabling an efficient suppression of electron-optical phonon coupling with a decelerated non-radiative rate. The presented study deepens the understanding of tailoring the photoluminescence properties of metal nanoclusters by manipulating surface trap chemistry and electron relaxation dynamics, which would shed new light on luminescent metal nanoclusters with customizable performance.