Highly efficient near-infrared phosphorescence from aggregated gold nanoclusters with humidity response

Luminescent gold nanoclusters (Au NCs) hold promises for various applications due to their unique optical properties. However, enhancing their near-infrared (NIR) photoluminescence quantum yield (QY) and elucidating the underlying emission mechanisms are challenging. In this study, we successfully synthesized glutathione-stabilized Au NCs (GSH-Au NCs) and achieved a NIR phosphorescence QY over 71% in solid. Time-resolved spectroscopy reveals that aggregation effectively suppresses structural vibrations and facilitates intersystem crossing (ISC), while modulation of the Au(0)/Au(I) ratio enhances radiative decay, presenting an effective strategy for improving the phosphorescence of Au NCs. Moreover, the resulting ultrabright GSH-Au NCs exhibit aggregation-induced emission tunable by humidity, demonstrating high potential as optical humidity sensors.