Hydrophobic ligand Influence on optical properties and hydrophilization process of core-shell quantum dots.

Abstract

Synthesized core-shell quantum dots (QDs) CdSe/CdS/ZnS with a relative quantum yield (QY) of 65%. Found that further hydrophilization of these QDs with mercapto acids by the ligand exchange method is not feasible, presumably due to the presence of 1-octanedthiol tightly bound to the QDs surface. Thus, 1-octanedthiol was excluded from the QDs synthesis procedure. Since the ligand exchange processes largely depend on the structure and composition of the nanocrystal surface, CdSe/ZnS QDs were further used as a model system. CdSe/ZnS QDs were obtained based on the same cadmium sulfide cores as the CdSe/CdS/ZnS QDs. The relative QY was 44%. The main difference between these QDs is the oleic acid presence on the surface instead of 1-octanethiol residues, which is easily replaced by hydrophilic mercapto acids during hydrophilization. CdSe/ZnS QDs were hydrophilized with 3-mercaptopropionic acid. Experimentally found the QDs required aliquot and the minimum required added ligand amount to ensure colloidal stability. The relative QY of the hydrophilized QDs ranged from 6 to 12%. To identify the QY decrease reasons of modified QDs, the luminescence lifetime (LLT) was determined and the radiative and nonradiative recombination constants were calculated. The LLT was 23±2 ns for QDs before hydrophilization and 16±1 ns for hydrophilized QDs. The constants change for QDs before and after hydrophilization is explained by a decrease in the ODs surface passivation degree. Thus, the problem of reducing the QY may be associated with the CdSe/ZnS QDs use as a model and can be eliminated by further synthesis process modification.

Speaker

Matlakhov Ivan Sergeevich
Saratov State University, Saratov
Russia

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