Water-soluble tiopronin monolayer-protected silver clusters (Ag MPCs), with 1.6 nm average diameter cores, exhibit visible luminescence at 500 nm with a quantum yield estimated near 10-4 when excited at 400 nm. The Ag MPCs become organic-soluble upon conversion to poly(ethylene glycol) quaternary ammonium salts of the carboxylates of the N-2-mercaptopropionylglycine ligand monolayer. The Ag MPC luminescence becomes more intense in nonpolar organic solvents. The luminescence may arise from interband recombination transitions between the d band and the sp conduction band. Atoms in the Ag MPC core can be replaced by An atoms via a galvanic metal exchange reaction between the silver clusters and Au(I)[SCH2(C6H4)CCH3)(3)]. The reaction was detected by observing the time-dependent change of the surface plasmon absorbance and emission spectra of the Ag MPC to spectra characteristic of An MPCs. The reaction was also assessed by transmission electron microscopy (TEM) and elemental analysis.