Enhancement of the alloyed CdZnSeS/ZnS quantum dots photoluminescence by thiol ligands capping

Most of the existing hydrophilization techniques for the semiconductor quantum dots (QDs) lead to degradation of photoluminescence (PL). Therefore, for the applying of QDs in the areas requiring their stability in water media (e.g. bio- and chemical analysis, labeling and sensing), it is often necessary to find a balance between high stability, good optical properties, and difficulty of acquiring. This article describes simple, fast, and easy scalable methods for alloyed CdZnSeS/ZnS QDs ligand exchange using 2-mercaptoethanol, thioglycolic, 3-mercaptorpopionic and dihydrolipoic acids. The proposed ligand exchange techniques provide the enhancement of the QDs photoluminescence intensity in contrast to most of other ligand exchange procedures on the QDs surface. In optimized conditions the twofold photoluminescence quantum yield increase compared to the initial hydrophobic CdZnSeS/ZnS QDs was achieved. Hydrophilized nanoparticles maintained colloidal stability for a period more than 13 months. The suggested mechanism of the PL increase is the passivation of the QDs surface with molecules containing a thiol group. The combination of the proposed effective CdZnSeS/ZnS QDs synthesis and modification methods shows the prospect of their implementation as basic luminescent material for a wide range of applications.