Nanotechnology Brightens the Future of Nanocrystal Lasers

Quantum dots’ prospects for use in laser applications are improved as a result of a study showing how to limit a deleterious effect that robs the semiconductor nanocrystals of their potential lasing power. In 2000, Los Alamos National Laboratory scientists and collaborators demonstrated that quantum dots could be made to lase (Science 290, 314; DOI:10.1126), a demonstration that showed potential applications in optics. Despite the proof‐of-principle experiment, nanocrystal lasing has remained impractical. Spatial confinement of electronic excitations in the seiconductor nanocrystals enhances a fast relaxation process known as Auger recombination. This recombination quenches the electronic excitations required for lasing and causes electron, rather than photon, emission. Now Laboratory scientists have published significant advances in understanding and controlling the Auger recombination process in nanocrystal quantum dots. This work could open the door to exciting new applications of nanocrystals in practical lasing technologies.

The research team discovered that coating a cadmium selenide (CdSe) quantum dot core with a few monolayer thick shell of cadmium sulfide (CdS) suppresses the Auger recombination enough to make lasing practical. Their research shows the importance of interfacial effects in Auger recombination. The scientists’ spectroscopic measurements indicate that the improvement is caused by the unique electronic properties of a few monolayer thin alloy layer at the core-shell interface ). The interfacial CdSeS alloy layer “smoothes” the nanocrystal confinement potential, a result that is consistent with theoretical predictions. This significant advance in Augersuppression strategies should help in the development of a new generation of nanocrystals with engineered interfaces for future lasing applications across a wide range of emission wavelengths.

The work was led by Victor Klimov of the Laboratory’s Chemistry Division and colleagues. Their work “Breakdown of Volume Scaling in Auger Recombination in CdSe/CdS Heteronanocrystals: The Role of the Core-Shell Interface,” was published in Nano Letters 11, 687 (2011). Chemical and Engineering News, the magazine published by the American Chemical Society. DOE’s Office of Basic Energy Sciences, which funds the Center for Integrated Nanotechnologies, Center for Advanced Solar Photophysics (Energy Frontier Research Center), and Single Investigator Small Group Award; and the Laboratory Directed Research and Development (LDRD) program funded different aspects of the work. More information on the research and the research team: http://quantumdot.lanl.gov/.