Brighter side of semiconductor nanocrystals: How to make defects useful
D. D. Sarma
Solid State & Structural Chemistry Unit Indian Institute of Science Bengaluru 560012, INDIA
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One of the most exciting properties of undoped semiconductor
nanoparticles is the photoluminescence that is spectacular both in terms
of its colour tunability and emission efficiency, based on quantum size
effects. However, self-absorption as well as susceptibility to surface
degradation are known to drastically affect the quantum efficiency of
such bandgap emissions, posing a serious challenge to any technological
exploitation of these materials. Emissions from dopants, particulary Mn
in doped II-VI semiconductors, however, are known to have negligible
self-absorption and resistance to degradation via surface reactions.
Unfortunately, these advantages were realised at a cost, with hardly any
tunability of the Mn emission till we recently introduced a novel way
to achieve this counter-intuitive tunability from an atom-like emission.1, 2, 3
In our search for such novel approaches to achieve tunable PL emissions
from semiconductor nanoparticles without the disadvantage of any
self-absorption, we have been intrigued by the question whether other
forms of defects, besides point defects as represented by atomic dopants
(e.g. Mn in II-VI semiconductors), can also be meaningfully used to
serve the purpose. The presence of defects, primarily surface defects,
in semiconductor nanocrystals has been recognized as one of the major
deterrents to achieve improved photoluminescence properties. Though it
provides a Stokes’ shifted PL emission, it affects adversely our ability
to control the emission wavelength and to improve the photoluminescence
efficiency. In addition to point defects, I shall present our
experimental realisations, supported by theoretical considerations, of
using “protected”, extended defects in semiconductor nanoparticles for
interesting PL properties.4
1. Hazarika A, Layek A, De S, Nag A, Debnath S, Mahadevan P, Chowdhury A, and Sarma D D, Phys. Rev. Lett. 2013, 110, 267401.
2. Hazarika A, Pandey A, and Sarma D. D., J. Phys. Chem. Lett. 2014, 5, 2208.
3. Hazarika A et al., Unpublished results.
4. Das S et al., Unpublished results.