Center for Functional Nanomaterials Seminar

Colloidal quantum dots (QDs) are small chunk of semiconductors which, due to quantum confinement, exhibit a number of fascinating properties. Bu varying the size and/or the composition of QDs, one can easily tune their photophysical properties, like the band gap width, absorption offset or luminescence peak wavelength. This extreme tunability make QDs attractive materials for modern optical and optoelectronic applications, including solar cells, luminescent solar concentrators, light-emitting diodes, and lasers. Moreover, colloidal QDs are solution-processable, which makes them a natural choice for flexible, wearable and/or disposable electronics. In the first part of my talk, I will present how engineered QDs can be used to create a solution-processable optically-pumped laser with extremely low lasing threshold. Conventional QDs are difficult to use in lasing because of complications associated with extremely short optical-gain lifetimes limited by nonradiative Auger recombination. Here, by combining compositional grading of the QD's interior for suppressing Auger decay with post-synthetic photochemical charging for removing parasitic ground-state absorption, we reduced the lasing threshold to sub-single-exciton-per-QD limit. As a favorable departure from traditional multi-exciton–based lasing schemes, our approach should facilitate the development of solution-processable lasing devices and thereby help to extend the reach of lasing technologies into areas not accessible with traditional, epitaxially grown semiconductor materials. In the second part, I will demonstrate unusual applications of manganese (Mn) doped QDs. In these systems, the exciton generated in a QD by an absorbed photon is quickly transferred to the Mn dopant, where the collected energy can be stored for desired intervals of time (up to milliseconds) even at room temperature. Additionally, the Mn-doped QDs feature strong spin-exchange interactions bet