Fluorescence from Molecular Silver Nanoparticles

Small metal nanoparticles are known to be much more fluorescent than larger plasmonic nanoparticles; however, the nature and origin of their fluorescence are not fully understood. Fluorescence is thought to originate from either the quantum states within the metal core or mixed ligand states at the inorganic–organic interface. Here we show that fluorescence from molecular silver glutathionate nanoparticles has its origin in interfacial electronic states. Fluorescence spectra were found to be independent of size, with very similar wavelength and bandwidth, although the quantum yield was not. Excitation spectra indicated that the strongest fluorescence had its origin in that part of the spectrum that is dominated by ligand-related states. Further, excitations to strictly core states and to higher lying d-band states had no apparent contribution to the fluorescence. Time-resolved spectroscopic measurements showed that Ag 32 (SG) 19 and Ag 15 (SG) 11 have a common emissive state, with the same emission wavelength and dynamic, which can be assigned to the metal–ligand state.