Concentration-Dependent Photoinduced Photoluminescence Enhancement in Colloidal PbS Quantum Dot Solution

Abstract

The concentration-dependent photoinduced photoluminescence (PL) enhancement of PbS quantum dots (QDs) is observed for the first time in the PbS colloidal solution. The enhancement in PL efficiency is attributed to the photooxidation of PbS QD surface based on the optical, transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) measurements. The decrease in PbS QD concentration leads to the increase in the amplitude of PL enhancement and to the decrease in the time required to reach the maximum PL enhancement. For the lowest investigated QD concentration of 58.7 nmol/L, PL efficiency can be increased by as much as 60 times. The critical concentration for realizing the considerable PL enhancement is found to be ∼200 nmol/L. Further investigation shows that the concentration-dependent PL enhancement is related to spontaneous ligand desorption and therefore more efficient photooxidation in low-concentration samples. Furthermore, it was found that the enhanced PL can remain during storage. It suggests that the postsynthesis treatment of UV illumination can serve as an alternative, while simple and highly efficient way in improving the PL efficiency of PbS QDs when the coverage of surface ligands is appropriately controlled.