Effect of Pb2+ Ions on Photoluminescence of ZnS-Coated AgInS2 Nanocrystals

The effect of quenching of photoluminescence (PL) intensity of thiol-stabilized water-soluble ZnS-coated AgInS2 nanocrystals (NCs) in the presence of Pb2+ ions is investigated. The factors influencing the efficiency of quenching process such as NCs dilution, pH value, composition, and concentration of working buffer solution are studied. It is found that the increasing of NCs dilution as well as the acidity of buffer solution promotes PL quenching by Pb2+ ions. In all media used, the decrease of PL intensity in the presence of Pb2+ ions is accompanied by a red shift of the PL band. In 0.5x10(-3)m citrate buffer solution, the red shift reached almost 5nm. The degradation of the PL intensity is attributed to formation of some substances at the NC surface acting as the centers of nonradiative recombination. The red shift is ascribed to different quenching effect of Pb2+ ions on the PL intensity of NCs of different sizes. The bimodal distribution of the NCs is proved by the PL study of NC fractions separated by ultracentrifugation. The obtained results could be useful for development of novel methods for detection of heavy metal ions.