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Light Conversion in Nanocrystal/2D Semiconductor Hybrids

September 14, 2018 | 11:00 a.m.
NH 203 | Seminar Flyer

Seminar Speaker

Anton Malko, Ph.D.

Associate Professor of Physics and Materials Science The University of Texas at Dallas

Abstract:

Monolayer transition metal dichalcogenides (TMD) such as MoS2, MoSe2, WSe2 constitute a new class of two-dimensional (2D) direct-gap semiconductors widely believed to be promising candidates for optoelectronic applications. Thanks to the 2D confinement and reduced dielectric screening, these systems support tightly-bound electron-hole pairs, excitons, which are prominently featured in their light absorption and emission spectra. However, the number of excitons produced in TMDs by a direct photoexcitation is restricted due to the limited amount of light absorption, fast recombination losses and associated low quantum yield. In our work, we demonstrate a 10-fold increase of MoS2 excitonic photoluminescence (PL) enabled non-radiative energy transfer (NRET) from the proximal quantum dots. The understanding of this effect is facilitated by our application of transient absorption (TA) spectroscopy to monitor the energy influx into the monolayer MoS2 in the process of ET from photoexcited CdSe/ZnS nanocrystals. In contrast to PL spectroscopy, TA can detect even non-emissive excitons, and we register an order of magnitude enhancement of the MoS2 excitonic TA signatures in hybrids with NQDs. The TA and PL data clearly illustrate the efficacy of MoS2 and likely other TMDC materials as energy acceptors and the possibility of their practical utilization in NRET-coupled hybrid nanostructures.

Bio:

Prof. Malko obtained a BS degree in physics and applied math from Moscow Institute of Physics and Technology, Russia in 1998, and a PhD in Physics/EE from New Mexico State University/Los Alamos National Laboratory, USA in 2002. He is an Associate Professor at the University of Texas at Dallas in Physics and Materials Science where he is the head of the optics and ultrafast spectroscopy laboratory.