Chemical Engineering April 2019 - 17

NajingTech
QD on chip
QLED electroluminescence
Composite QLCF
without barrier film
Roadmap (NajingTech)
QD/NC
materials
2002
QLCF with high
cost barrier film
2016
2017
2018
Year
FIGURE 5. Refining electroluminescent properties is the next step in implementing
QDs into more complex LED applications
photovoltaics, LEDs, lasers, bio-imaging and more. To
facilitate such a wide range of end uses, ensuring consistency
in surface chemistry and other functional properties
is critically important. " Composition, size and geometry
are all important factors that are customized to
fit all of these diverse applications, " says Bryce Nelson,
head of materials science at MilliporeSigma. " For example,
PbS-based QDs exhibit fluorescence in the infrared
regime, while InP/ZnS and Cd-based QDs possess
fluorescence emission in the ultraviolet-visible range.
Adjustments in size allow the fine-tuning of fluorescence
properties, " he continues. And depending on the end
market, further customization may be required, such as
optimizing surface chemistry for compatibility with a surrounding
polymer or matrix in display applications. The
QD synthesis method is also critical in tailoring materials
for new end-use applications - common techniques include
the hot-injection method and the heat-up method,
among many others.
" Solar cells and lasers come to mind as areas with a
lot of research activity right now. For in-vivo applications,
QDs with infrared emission capabilities enable enhanced
single-cell imaging, as well as deep-tissue mono- and
multi-photon imaging, " says Nelson. However, he emphasizes
that the use of QDs in-vivo is still hampered by
challenges related to toxicity and lack of biodegradability,
further highlighting the importance of reducing heavymetal
content. According to Nelson, the Performance
Materials business of Merck is working toward Cd-free
QDs for display applications, which can provide the increased
color range of QDs without the toxicity of heavy
metals. EMD Performance Materials is also currently developing
new QD technologies for next-generation organic
LED (OLED) displays, which will require complex
chemical formulations to vastly improve color quality.
While these new technologies, says Nelson, are still a
few years from commercialization and significant formulation
challenges remain, the combination of OLED and
QD technologies has the potential to bring a new standard
of performance in terms of brightness, efficiency
and viewing angle.
From displays to biomedical imaging to solar energy
and agriculture, the flurry of activity around tailoring QDs
for ever-expanding application fields is certainly going to
continue in the coming years, with an increasing number
of novel end-uses expected to appear, as formulation
and synthesis techniques are further honed. ■
Mary Page Bailey
CHEMICAL ENGINEERING WWW.CHEMENGONLINE.COM
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Chemical Engineering April 2019

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