Speaker: Prof. Anton Malko, PhD
of Physics and Materials Science, the University of Texas at Dallas
Date & Time: Tuesday May 9th, 2017 at 1pm
Venue: Building 3, level 5, room 5209
Light refreshments will be provided.
Abstract: Artificially structured nanoscale
materials have attracted immense attention in scientific and technical
communities during past decades due to the potential for controlling their optical,
electronic and chemical properties. In particular, CdSe semiconductor
nanocrystals quantum dots (NQDs) represent a class of quasi-zero-dimensional
objects in which the motion of carriers is restricted in all 3 dimensions. Bulk
crystalline structure in preserved in NQDs, but due to 3D quantum confinement,
NQDs have discrete atomic-like absorption and emission spectra, which are
strongly size dependent.
To successfully apply
nanocrystals in a variety of optoelectronics applications, one needs to
thoroughly understand and engineer dynamics of strongly correlated electron-hole
pairs, namely excitons (X) and multiexcitons (MX). Dynamics of excitons are
often affected by the presence of surface-related states and interactions with
the substrates, while those of MXs are governed by non-radiative, Auger-type
interactions. The latter is strongly affecting the performance of NQDs in a
variety of applications, ranging from single particle photoluminescence (PL)
emission to optical gain and lasing in NQD solids. One aspect of our recent
work concerns the issue of single NQD PL intermittence or “blinking” in giant
CdSe/CdS multishell nanocrystals with strongly suppressed Auger recombination.
We have recently shown that progressive addition of CdS shells leads to strong
modifications of Auger rates, blinking suppression and appearance of higher
order MX states in the PL emission spectra. These observations allowed us to
propose an ingenuous mechanism explaining evolution of the exciton and multiexciton
populations in g-NQDs and would aid the development of the new types of
optoelectronic devices that rely on the controlled emission of single photons
such as for quantum information/ computing and biomedical imaging/therapeutics.
On the other side, we have developed hybrid multifunctional nanostructures by combining strongly absorbing NQD components with high-mobility semiconductors
(silicon and 2D atomic layers). In such hybrid systems, the
excitonic energy is transferred via non-radiative (NRET) and radiative
(RET) energy coupling across the interface with the subsequent separation and
transport of charge carriers entirely within the semiconductor-based component.
Our results show promise for the development of the efficient, thin film,
ET-based hybrid structures for photovoltaic applications. Biography: