Seedless Continuous Injection Synthesis of IndiumPhosphide Quantum Dots as a Route to Large Size and Low Size Dispersity
2020
Because
of their lower toxicity, indium phosphide (InP) quantum
dots (QDs) are replacing cadmium selenide QDs in applications that
require narrowband luminescence across the visible spectrum. However,
InP QDs generally suffer from lower size tunability and broader ensemble
emission linewidths because of imperfect synthetic control of nucleation
and growth. Despite evidence that InP QDs do not follow the mechanisms
that hot-injection and heat-up syntheses were designed to facilitate,
these methods are still used, at least as the first step, in most
syntheses of InP QDs. In this article,
we describe a new method to synthesize large InP QDs with low size
dispersity that does not require a hot-injection or heat-up step.
Instead, nucleation, growth, and size focusing all take place continuously
during a slow syringe-pump-mediated continuous injection of precursors
into the reaction mixture. In refining our method, we monitored the
photoluminescence (PL) and absorption spectra to find indirect evidence
for the role of persistent intermediates in the formation of a secondary
population of smaller QDs. We then developed a growth model that is
consistent with our observations, and we used it to improve our method
with a variable-rate injection that controls the concentration of
intermediates to extend growth and prevent secondary nucleation. The
result was InP QDs with an absorption peak at 631 nm with a half width
at half-maximum of 81 meV. Growth of a thin zinc selenide shell on
these InP QDs revealed a PL peak centered at 655 nm with a full width
at half-maximum of 53 nm. These values are indicative of large QDs
with low size dispersity. This work demonstrates a new method to synthesize
large InP QDs that may be attractive to large-scale industrial processes
because of its simplicity and potential scalability.
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