The integration of metal atoms and clusters in well-defined dielectric cavities is a powerful strategy to impart new properties to them that depend on the size and geometry of the confined space as well as on metal–host electrostatic interactions. Here, we unravel the dependence of the electronic properties of metal clusters on space confinement by studying the ionization potential of silver clusters embedded in four different zeolite environments over a range of silver concentrations. Extensive characterization reveals a strong influence of silver loading and host environment on the cluster ionization potential, which is also correlated to the cluster’s optical and structural properties. Through fine-tuning of the zeolite host environment, we demonstrate photoluminescence quantum yields approaching unity. This work extends our understanding of structure–property relationships of small metal clusters and applies this understanding to develop highly photoluminescent materials with potential applications in optoelectronics and bioimaging.

Unmasking the glow of silver clusters: Small silver clusters stabilized by organic materials or inorganic surfaces can exhibit bright photoluminescence, but the origin of this effect has been difficult to establish, in part because the materials are heterogeneous and contain many larger but inactive clusters. Grandjean et al. studied silver clusters in zeolites, using x-ray excited optical luminescence to monitor only the emissive structures (see the Perspective by Quintanilla and Liz-Marzán). Aided by theoretical calculations, they identified the electronic states of four-atom silver clusters bound with water molecules that produce bright green emission—thus identifying candidate materials for application in lighting, imaging, and therapeutics. Science , this issue p. 686 ; see also p. 645

The synthesis and characterization of LTA(Li)–Ag zeolites with water-responsive photoluminescence properties and high external quantum efficiencies is described in this study.