Colloidal quantum dots (CQDs) have huge potential in different application fields, as novel light sources, photoluminescent probes and in solar energy conversion. However, their sensitivity to the surrounding environment and the presence of surface defects affect their photoluminescent properties and restrict their widespread deployment. Post-synthetic treatment of CQDs has previously been introduced as a strategy to overcome this barrier, particularly in aqueous thiol-capped CdTe CQDs. After demonstrating the synthesis of high-quality CdTe CQDs using a mixed ligand system, this work presents the effects of post-synthetic surface treatment by using chloride and bicarbonate ions, resulting in marked suppression of non-radiative recombination and more than two-fold increase (from 30 % to 76 %) of the photoluminescence quantum yield (PL QY). The effect of the treatment was characterized by absorption and PL spectroscopy, dynamic light scattering (DLS), time-correlated single photon counting (TCSPC) PL decay measurements and transmission electron microscopy (TEM). Time-resolved PL measurements in combination with calculated PL QYs indicated an increase in the radiative PL lifetime after salt treatment. This strategy slightly increased the hydrodynamic shell around the CQDs and provided stronger repulsive electrostatic forces by enhancing the surface charge. The optimized concentration and chosen ratio of thiol ligands represented in this work were proven to work for different sizes of CdTe CQDs. Combining these beneficial effects with tunable CQD emission and high extinction coefficients leads to robust and strongly-emitting advanced materials that can be used as a color enhancement in display backlight1.
1Schneider J., Dudka T, Xiong, Y. Wang Z., Gaponik N., and Andrey L. Rogach. Aqueous-Based Cadmium Telluride Quantum Dot/Polyurethane/Polyhedral Oligomeric Silsesquioxane Composites for Color Enhancement in Display Backlights. J. Phys. Chem. C, Dec 2017, Article ASAP