报告人：Victor I. Klimov 教授
Chemically synthesized quantum dots (QDs) can potentially enable a new class of highly flexible lasers processible from solutions without complications associated with vacuum-based epitaxial techniques. Colloidal QDs feature near-unity emission quantum yields and widely tunable emission wavelengths controlled by their size and/or composition. Further, a wide separation between electronic levels and low degeneracies of band-edge states reduce the lasing threshold and enhance temperature stability compared to semiconductor quantum wells used in traditional laser diodes. Despite a considerable progress over the past years, colloidal-QD lasing is still at the laboratory stage and an important challenge - realization of lasing with electrical injection - is still unresolved. A major complication, which hinders the progress in this field, is fast nonradiative Auger recombination of gain-active multi-carrier species. Recently, we explored several approaches for mitigating the problem of Auger decay by taking advantage of a new generation of core/multi-shell QDs with a radially graded composition that allow for considerable (nearly complete) suppression of Auger recombination by “softening” the electron and hole confinement potentials. Using these specially engineered QDs, we have been able to achieve two important milestones in the QD field, that is, the first demonstration of continuous-wave colloidal-QD lasing with optical excitation and the first realization of optical gain in colloidal nanostructures with direct-current electrical pumping. Further, using these new QDs, we have been able to practically demonstrated the viability of a “zero-threshold-optical-gain” concept using not neutral but negatively charged particles wherein the pre-existing electrons block either partially or completely ground-state absorption. Such charged QDs are optical-gain-ready without excitation and, in principle, can exhibit lasing at vanishingly small pump levels. All of these exciting recent developments demonstrate a considerable promise of colloidal nanomaterials for implementing solution-processible optically and electrically pumped laser devices operating at virtually any wavelength using a verity of optical cavity designs. These materials are also ideally suited for the realization of novel concepts such as laser lighting and displays, on-chip optical interconnects, and multidimensional laser arrays.
Victor I. Klimov is a Fellow of Los Alamos National Laboratory and Director of the Center for Advanced Solar Photophysics of the U.S. Department of Energy. He received his M.S. (1978), Ph.D. (1981), and D.Sc. (1993) degrees from Moscow State University. He is a Fellow of both the American Physical Society and the Optical Society of America, and a recipient of the Humboldt Research Award. His research interests include photophysics of semiconductor nanocrystals, and fundamental aspects of solar cells, LEDs, and lasers based on semiconductor nanomaterials.