Highly Luminescent Water-Dispersible NIR-Emitting Wurtzite CuInS₂/ZnS Core/Shell Colloidal Quantum Dots

Abstract

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 Cu2-xS nanocrystals (NCs), which are converted by topotactic partial Cu+ for In3+ exchange into CIS NCs. These NCs are subsequently used as cores for the overgrowth of ZnS shells (≤1 nm thick). The CIS/ZnS core/shell QDs exhibit PL tunability from the first to the second NIR window (750–1100 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.

Size-Dependent Band-Gap and Molar Absorption Coefficients of Colloidal CuInS2 Quantum Dots

“…Nevertheless, it is clear that the band gap of wz CIS is smaller than that of cp CIS, which explains why wz CIS QDs typically show PL at lower energies than similarly sized cp CIS QDs. 58,68 This is also consistent with the expression obtained by fitting the experimental data for cp CIS QDs (Figure 4b) to eq 2 (χ 2 ≈ 0.9997):which yields a E g (∞) value that agrees very well with the band gap reported for bulk cp CIS ( viz ., 1.535 eV at 300 K). 79 We note that some data points (indicated by the dashed ellipsoid in Figure 4b) were not included in the fit because they clearly deviated from the general trend evidenced by the other data points.…”

“…58 The product CIS QDs inherit the shape, size, and polydispersity of the template Cu 2– x S NCs (Figure 1b,c). High-resolution transmission electron microscopy (HRTEM) (Figure 1c) and X-ray diffraction (XRD) [Supporting Information (SI), Figure S1] show that the product CIS QDs have the wurtzite crystal structure, demonstrating that the hexagonal sulfide sublattice of the template Cu 2- x S NCs is preserved in the product NCs, in agreement with previous reports.…”

Cytotoxicity, fluorescence tagging and gene-expression study of CuInS/ZnS QDS - meso (hydroxyphenyl) porphyrin conjugate against human monocytic leukemia cells

“…Amid these QDs, much attention has been given to CuInS based QDs 10 . Interest in ternary QDs lies in their reduced toxicity; size-and composition -tunable photoluminescence properties [11][12][13] , high Stokes shift and long fluorescence lifetime all which has legitimated their use in biological applications such as biomedical imaging and drug delivery 14,15 . The conjugation of nanomaterials such as quantum dots (QDs) to porphyrins has been reported as an improvement on the biological application of porphyrins in treatment modalities such as photodynamic therapy (PDT) where porphyrins have been most applicable.…”

CuInS2–In2Se3 quantum dots – a novel material via a green synthesis approach

“…30 Most of the reported works on CIS and CISe QDs are based on growing a ZnS passivating layer over the core to form a core/shell type-I structure. 17,[31][32][33] In some earlier attempts, In 2 S 3 was used in conjunction with CIS thin lms for improving the performance of thin lm based photovoltaic systems. 34,35 Also, In 2 Se 3 has been employed as a buffer layer in devising CIS QD sensitized solar cells.…”

“…18,39,40 The advantage of the colloidal method lies in its control of particle size and shape distribution with less number of defect states. 33,37,41,42 Developing green chemistry alternatives in nanomaterials synthesis is a major concern of the research community. 43 In our synthesis, to avoid the toxicity caused by the organophosphines, we dissolved the elemental selenium in the capping agent-coordinating solvent (oleylamine-octadecene) mixture.…”