Efficient, Stable, and Photoluminescence Intermittency-Free CdSe-Based Quantum Dots in the Full-Color Range

Colloidal semiconductor CdSe-based quantum dots (QDs) show undesirable photoluminescence (PL) intermittency with frequent and long-lasting dark states due to positively charged states, significantly limiting QD optoelectronic and photonics applications. Here, we show that p-phenylenediamine (PPD) can completely suppress the long-lasting dark states in the PL intensity trajectories for single CdSe-based QDs in the full-color emission range from 459 to 800 nm, while hardly influencing any other PL properties of the QDs, such as the PL intensity, lifetime, and emission spectra. The suppression mechanism is investigated by comparing PPD to another amine compound, N,N-dimethylaniline. With a reasonable highest occupied molecular orbital energy, PPD facilitates electron transfer from PPD to the positively charged QDs, thus, neutralizing the extra hot holes via an Auger-assisted process. Therefore, the positively charged states of QDs and the PL intermittency could be eliminated. Moreover, we demonstrate that PPD can effectively suppress the photobleaching of CdSe-based QDs, and the average survival time of single QDs can be extended from a few minutes to more than 1 h. Finally, we demonstrate the application of PPD-stabilized QDs to single-particle tracking and HeLa cell imaging under relevant biological conditions and show their promising potential in various biomedical applications.