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2016 ; 49
(5
): 902-10
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Colloidal Double Quantum Dots
#MMPMID27108870
Teitelboim A
; Meir N
; Kazes M
; Oron D
Acc Chem Res
2016[May]; 49
(5
): 902-10
PMID27108870
show ga
Pairs of coupled quantum dots with controlled coupling between the two potential
wells serve as an extremely rich system, exhibiting a plethora of optical
phenomena that do not exist in each of the isolated constituent dots. Over the
past decade, coupled quantum systems have been under extensive study in the
context of epitaxially grown quantum dots (QDs), but only a handful of examples
have been reported with colloidal QDs. This is mostly due to the difficulties in
controllably growing nanoparticles that encapsulate within them two dots
separated by an energetic barrier via colloidal synthesis methods. Recent
advances in colloidal synthesis methods have enabled the first clear
demonstrations of colloidal double quantum dots and allowed for the first
exploratory studies into their optical properties. Nevertheless, colloidal double
QDs can offer an extended level of structural manipulation that allows not only
for a broader range of materials to be used as compared with epitaxially grown
counterparts but also for more complex control over the coupling mechanisms and
coupling strength between two spatially separated quantum dots. The photophysics
of these nanostructures is governed by the balance between two coupling
mechanisms. The first is via dipole-dipole interactions between the two
constituent components, leading to energy transfer between them. The second is
associated with overlap of excited carrier wave functions, leading to charge
transfer and multicarrier interactions between the two components. The magnitude
of the coupling between the two subcomponents is determined by the detailed
potential landscape within the nanocrystals (NCs). One of the hallmarks of double
QDs is the observation of dual-color emission from a single nanoparticle, which
allows for detailed spectroscopy of their properties down to the single particle
level. Furthermore, rational design of the two coupled subsystems enables one to
tune the emission statistics from single photon emission to classical emission.
Dual emission also provides these NCs with more advanced functionalities than the
isolated components. The ability to better tailor the emission spectrum can be
advantageous for color designed LEDs in lighting and display applications. The
different response of the two emission colors to external stimuli enables
ratiometric sensing. Control over hot carrier dynamics within such structures
allows for photoluminescence upconversion. This Account first provides a
description of the main hurdles toward the synthesis of colloidal double QDs and
an overview of the growing library of synthetic pathways toward constructing
them. The main discoveries regarding their photophysical properties are then
described in detail, followed by an overview of potential applications taking
advantage of the double-dot structure. Finally, a perspective and outlook for
their future development is provided.
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