Colloidal Synthesis of PbS and PbS/CdS Nanosheets Using Acetate-Free Precursors

New methods are developed for the synthesis and surface modification of colloidal PbS nanosheets. We find that residual acetate is a crucial reagent for the formation of PbS nanosheets by existing syntheses. The amount of acetate in reaction mixtures is, however, difficult to control, which substantially reduces the reproducibility of the synthesis. To solve this problem, we develop an acetate-free synthetic method to yield colloidal PbS nanosheets with lateral dimensions of several hundred nanometers. The thickness and shape of PbS nanosheets can be readily tuned by varying the synthetic parameters. Assynthesized nanosheets have a photoluminescence quantum yield of around 6%. Time-resolved photoluminescence spectroscopy shows that the carrier decay in nanosheets is not a single exponential but involves surface defect states as well as multiple carrier interactions. The surfaces of PbS nanosheets can be modified by reaction with Cd(OA)(2). Atomic resolution electron microscopy reveals the formation of PbS/CdS core/shell nanostructures, and the photoluminescence quantum yield of PbS/CdS nanosheets reaches about 11%.