The photoluminescence of metal nanoclusters is typically low, and phosphorescence emission is rare due to ultrafast free-electron dynamics and quenching by phonons. Here, we report an electronic engineering approach to achieving very high phosphorescence (quantum yield 71.3%) from a [Au@Cu14(SPhtBu)12(PPh(C2H4CN)2)6]+ nanocluster (abbreviated Au@Cu14) in non-degassed solution at room temperature. The structure of Au@Cu14 has a single-Au-atom kernel, which is encapsulated by a rigid Cu(I) complex cage. This core-shell structure leads to highly efficient singlet-to-triplet intersystem crossing and suppression of nonradiative energy loss. Unlike the phosphorescent organic materials and organometallic complexes—which require de-aerated conditions due to severe quenching by air (i.e., O2)—the phosphorescence from Au@Cu14 is much less sensitive to air, which is important for lighting and biomedical applications.
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