The physical and chemical properties of silver are highly dependent on their size, in particular in the nanometer range. Bulk silver is electrically conducting and a good optical reflector due to the sea of freely moving delocalized electrons in the conduction band. On the other hand, silver nanoparticles display various colours due to surface plasmon resonance. Silver nanoclusters (Ag NCs) have attracted much research interest because of their unique size-dependent optical, electronic, magnetic, and catalytic properties that bridge the gap between small molecules (e.g. organometallic compounds) and bulk crystals (diameter typically >2 nm). As the size of silver nanoparticles decreases to the Fermi wavelength of an electron, discrete energy levels begin to form, and interactions with light lead to electronic transitions between different energy levels and strong photoluminescence. In fact, various studies have shown luminescent Ag NCs, which also demonstrate unique catalytic activity that varies strongly with the size of the nanoparticles. For instance, recent studies have demonstrated that Ag NCs might combine with oxygen to form a Ag NC and oxygen complex due to spin accommodation, which may be exploited for the catalysis of oxygen reduction reactions.¹