Green synthesis of strongly luminescent, ultrasmall pbs and pbse quantum dots

Abstract

Although size tunable synthesis of PbS between 3 and 10 nm with emission in the NIR. II region is well-known, there is no well-established method to produce smaller particles with emission below 1000 nm, which is easier to detect with less costly and more widely available Si and extented PMT-detectors. Here, we demonstrate synthesis of PbS QDs in sizes between 2.4 and 3.2 nm using PbCl2, elemental S, dodecanethiol (DT), and a toluene/oleylamine mixture at low temperatures (65-80 C-omicron). It was shown that addition of DT enhances the solubility of S and DT binds to the crystal surface during the growth, hence reducing the size with enhanced luminescence intensity. Use of toluene as a cosolvent reduces the viscosity and provides an additional reduction in the size. Using these variables, size tunable synthesis of highly luminescent QDs were achieved. Furthermore, we applied additional DT ligand exchange as a postprocess that increases the long-term stability of particles. The photoluminescence lifetime investigation provided insight into the luminescence properties of OLA/DT and DT-capped PbS QDs. Finally, we successfully expanded our synthesis method to the synthesis of small PbSe QDs.