Fluorescent AuAg alloy clusters: synthesis and SERS applications

Fluorescent metal nanoclusters have recently emerged as a new class of functional materials because of their potential in photocatalysis, water splitting, light harvesting and other applications. Herein, we demonstrate the synthesis of highly blue luminescent AuAg bimetallic alloy clusters using a simple one pot bottom up method. Transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and photoluminescence (PL) have been used to characterize the alloy clusters. A dramatic blue shift of the PL peak (from 608 nm to 444 nm) reveals a drastic change in the electronic transitions in the presence of Ag+, due to the formation of a new cluster. We have given emphasis to the influence of the capping ligand, pH and metal ions on the formation of the clusters and their stability. Based on controlled experiments and galvanic theory, an anti-galvanic reaction mechanism has been proposed for the formation of the bimetallic AuAg alloy clusters. The Surface Enhanced Raman Scattering (SERS) intensity is found to be increased in the presence of the AuAg alloy clusters and the enhancement factor (EF) is found to be 1.44 x 10(6) for the AuAg alloy nanocluster.