Professor Todd D. Krauss of the University of Rochester is supported by the Macromolecular, Supramolecular, and Nanochemistry (MSN) Program in the Division of Chemistry to synthesize graded core-shell CdZnSe/ZnSe quantum dots (QDs) and to characterize their structural and photophysical properties using a suite of analytical spectroscopic and microscopic techniques. It is expected that the photoluminescence (PL) blinking of individual quantum dots will be mitigated through the synthesis of QD structures having smooth potential energy variations across the QD. Such a QD structure is expected to reduce non-radiative Auger-type processes, which are believed to be a leading cause of PL blinking.
Despite over a decade of research, the root cause of an intermittent "blinking" of the photoluminescence of semiconductor QDs remains elusive. The overarching goal of this research is to understand fundamental causes of the blinking phenomenon, which will eventually lead to the mitigation of blinking altogether. Blinking severely limits the usefulness of QDs in applications that require the continuous output of single photons. For example, new cures for disease may be eventually discovered through the significant advances in single-protein fluorescent labeling and tracking enabled by non-blinking QDs. The proposed research also provides for the education and training of the next generation of physical chemists, inclusive of women and underrepresented minorities. The accomplishments of women graduate students and postdocs in chemistry will be highlighted on a specifically created website at the University of Rochester.
Semiconductor quantum dots are tiny inorganic particles that have the potential to revolutionize technology in several fields including solar cells, efficient solid-state lighting, medicine and medical devices, and the production of green fuels from sunlight. However, the synthesis of these nanoparticles is poorly understood, which has partially contributed to their inability to find a commercial application for several decades. We have discovered the fundamental reaction mechanism for synthesis of several kinds of semiconductor quantum dots, thus solving a 30-year old puzzle. We have also used this knowledge to improve the synthesis of these nanoparticles such that we can have much higher reproducibility and can in principle create much more advanced and highly engineered nanoparticles (Figure 1). We have also made discoveries in understanding how these novel nanoparticles interact with pulsed light versus light that is on all the time (called continuous wave light). We found that even for the same power of laser, pulsing the laser degrades the quantum dots much quicker than using continuous wave lasers (Figure 2). This finding is important as many researchers use pulsed lasers to study their nanoparticles and they may be inadvertently damaging the materials they are trying to study. Our findings have several broad implications for the use of quantum dots in real-world technology. For example, we discovered methods to make quantum dots reliably and reproducibly on a scale 1000 times larger than what is typically done. This could drive the price for quantum dots down from tens to hundreds of thousands of dollars per gram to less than one dollar per gram. Therefore, quantum dots are now potentially quite affordable and should find increased use in applications such as solar cells or solid state lighting. In our particular case we have explored the use of highly fluorescent quantum dots to improve medical devices.
