4 research outputs found
Highly Luminescent Water-Dispersible NIR-Emitting Wurtzite CuInS<sub>2</sub>/ZnS Core/Shell Colloidal Quantum Dots
Copper indium sulfide
(CIS) quantum dots (QDs) are attractive as
labels for biomedical imaging, since they have large absorption coefficients
across a broad spectral range, size- and composition-tunable photoluminescence
from the visible to the near-infrared, and low toxicity. However,
the application of NIR-emitting CIS QDs is still hindered by large
size and shape dispersions and low photoluminescence quantum yields
(PLQYs). In this work, we develop an efficient pathway to synthesize
highly luminescent NIR-emitting wurtzite CIS/ZnS QDs, starting from
template Cu<sub>2â<i>x</i></sub>S nanocrystals (NCs),
which are converted by topotactic partial Cu<sup>+</sup> for In<sup>3+</sup> exchange into CIS NCs. These NCs are subsequently used as
cores for the overgrowth of ZnS shells (â€1 nm thick). The CIS/ZnS
core/shell QDs exhibit PL tunability from the first to the second
NIR window (750â1100 nm), with PLQYs ranging from 75% (at 820
nm) to 25% (at 1050 nm), and can be readily transferred to water upon
exchange of the native ligands for mercaptoundecanoic acid. The resulting
water-dispersible CIS/ZnS QDs possess good colloidal stability over
at least 6 months and PLQYs ranging from 39% (at 820 nm) to 6% (at
1050 nm). These PLQYs are superior to those of commonly available
water-soluble NIR-fluorophores (dyes and QDs), making the hydrophilic
CIS/ZnS QDs developed in this work promising candidates for further
application as NIR emitters in bioimaging. The hydrophobic CIS/ZnS
QDs obtained immediately after the ZnS shelling are also attractive
as fluorophores in luminescent solar concentrators
Near-Infrared-Emitting CuInS<sub>2</sub>/ZnS Dot-in-Rod Colloidal Heteronanorods by Seeded Growth
Synthesis
protocols for anisotropic CuInX<sub>2</sub> (X = S, Se,
Te)-based heteronanocrystals (HNCs) are scarce due to the difficulty
in balancing the reactivities of multiple precursors and the high
solid-state diffusion rates of the cations involved in the CuInX<sub>2</sub> lattice. In this work, we report a multistep seeded growth
synthesis protocol that yields colloidal wurtzite CuInS<sub>2</sub>/ZnS dot core/rod shell HNCs with photoluminescence in the NIR (âŒ800
nm). The wurtzite CuInS<sub>2</sub> NCs used as seeds are obtained
by topotactic partial Cu<sup>+</sup> for In<sup>3+</sup> cation exchange
in template Cu<sub>2â<i>x</i></sub>S NCs. The seed
NCs are injected in a hot solution of zinc oleate and hexadecylamine
in octadecene, 20 s after the injection of sulfur in octadecene. This
results in heteroepitaxial growth of wurtzite ZnS primarily on the
Sulfur-terminated polar facet of the CuInS<sub>2</sub> seed NCs, the
other facets being overcoated only by a thin (âŒ1 monolayer)
shell. The fast (âŒ21 nm/min) asymmetric axial growth of the
nanorod proceeds by addition of [ZnS] monomer units, so that the polarity
of the terminal (002) facet is preserved throughout the growth. The
delayed injection of the CuInS<sub>2</sub> seed NCs is crucial to
allow the concentration of [ZnS] monomers to build up, thereby maximizing
the anisotropic heteroepitaxial growth rates while minimizing the
rates of competing processes (etching, cation exchange, alloying).
Nevertheless, a mild etching still occurred, likely prior to the onset
of heteroepitaxial overgrowth, shrinking the core size from 5.5 to
âŒ4 nm. The insights provided by this work open up new possibilities
in designing multifunctional Cu-chalcogenide based colloidal heteronanocrystals
Highly Luminescent (Zn,Cd)Te/CdSe Colloidal Heteronanowires with Tunable ElectronâHole Overlap
We report the synthesis of ultranarrow (Zn,Cd)ÂTe/CdSe
colloidal
heteronanowires, using ZnTe magic size clusters as seeds. The wire
formation starts with a partial Zn for Cd cation exchange, followed
by self-organization into segmented heteronanowires. Further growth
occurs by inclusion of CdSe. The heteronanowires emit in the 530 to
760 nm range with high quantum yields. The electronâhole overlap
decreases with increasing CdSe volume fraction, allowing the optical
properties to be controlled by adjusting the heteronanowire composition
Highly Luminescent (Zn,Cd)Te/CdSe Colloidal Heteronanowires with Tunable ElectronâHole Overlap
We report the synthesis of ultranarrow (Zn,Cd)ÂTe/CdSe
colloidal
heteronanowires, using ZnTe magic size clusters as seeds. The wire
formation starts with a partial Zn for Cd cation exchange, followed
by self-organization into segmented heteronanowires. Further growth
occurs by inclusion of CdSe. The heteronanowires emit in the 530 to
760 nm range with high quantum yields. The electronâhole overlap
decreases with increasing CdSe volume fraction, allowing the optical
properties to be controlled by adjusting the heteronanowire composition