Au ₂₀ Ag ₃₂ Nanocluster Emitting Bright Near-Infrared-II Photoluminescence with Quantum Yield of 30% in Aerated Solution

Atomically precise metal nanoclusters (NCs) have emerged as an important class of materials for optoelectronic applications, owing to their near-infrared-II (NIR-II) photoluminescence (PL) properties. To fully realize their applications, the PL quantum yield (PLQY) of NCs must be enhanced. In this regard, structure-property correlation studies are of critical importance. Herein, we report an alkynide-protected Au₂₀Ag₃₂ NC (charge neutral) protected by 36 ligands, including 12 Cl⁻ and 24 p-tert-butylphenylacetylide (tBuPA⁻). Structural analysis shows that the NC is a three-dimensional growth of a bi-icosahedral core. Theoretical analysis reproduces the experimental optical absorption spectral features. Interestingly, Au₂₀Ag₃₂ shows bright PL emission centered at 980 nm, with a PLQY of 30% in aerated and 33% in deaerated medium at room temperature, which is the highest among the reported NIR-II NCs. Furthermore, cryogenic PL measurements and transient absorption spectroscopy analysis reveal the PL mechanism, which involves both thermally activated delayed fluorescence (TADF) and phosphorescence (PH). This study is expected to motivate further research in expanding the Au-Ag nanoclusters and studying their high NIR-II emission.