Despite broad applications
in imaging, energy conversion, and telecommunications,
few nanoscale moieties emit light efficiently in the shortwave infrared
(SWIR, 1000–2000 nm or 1.24–0.62 eV). We report quantum-confined
mercury chalcogenide (HgX, where X = Se or Te) nanoplatelets (NPLs)
can be induced to emit bright (QY > 30%) and tunable (900–1500+
nm) infrared emission from attached quantum dot (QD) “defect”
states. We demonstrate near unity energy transfer from NPL to these
QDs, which completely quench NPL emission and emit with a high QY
through the SWIR. This QD defect emission is kinetically tunable,
enabling controlled midgap emission from NPLs. Spectrally resolved
photoluminescence demonstrates energy-dependent lifetimes, with radiative
rates 10–20 times faster than those of their PbX analogues
in the same spectral window. Coupled with their high quantum yield,
midgap emission HgX dots on HgX NPLs provide a potential platform
for novel optoelectronics in the SWIR.
The influence of external dielectric
environments is well understood
for 2D semiconductor materials but overlooked for colloidally grown
II–VI nanoplatelets (NPLs). In this work, we synthesize MX
(M = Cd, Hg; X = Se, Te) NPLs of varying thicknesses and apply the
Elliott model to extract exciton binding energiesreporting
values in good agreement with prior methods and extending to less
studied cadmium telluride and mercury chalcogenide NPLs. We find that
the exciton binding energy is modulated both by the relative effect
of internal vs external dielectric and by the thickness of the semiconductor
material. An analytical model shows dielectric screening increases
the exciton binding energy relative to the bulk by distorting the
Coulombic potential across the NPL surface. We further confirm this
effect by decreasing and recovering the exciton binding energy of
HgTe NPLs through washing in polarizable solvents. Our results illustrate
NPLs are colloidal analogues of van der Waals 2D semiconductors and
point to surface modification as an approach to control photophysics
and device properties.
Coordination polymers (CPs) supporting tunable through-framework conduction and responsive properties are of significant interest for enabling a new generation of active devices. However, such architectures are rare. We report a redox-active CP composed of two-dimensional (2D) lattices of coordinatively bonded Mo(INA) clusters (INA = isonicotinate). The 2D lattices are commensurately stacked and their ordering topology can be synthetically tuned. The material has a hierarchical pore structure (pore sizes distributed between 7 and 33 Å) and exhibits unique CO adsorption (nominally Type VI) for an isotherm collected at 195 K. Furthermore, cyclic voltammetry and electrokinetic analyses identify a quasi-reversible feature at E = -1.275 V versus ferrocene/ferrocenium that can be ascribed to the [Mo(INA)] redox couple, with an associated standard heterogeneous electron transfer rate constant k = 1.49 s. The tunable structure, porosity, and redox activity of our material may render it a promising platform for CPs with responsive properties.
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