Colloidal Gradated Alloyed (Cu)ZnInS/ZnS Core/Shell Nanocrystals with Tunable Optical Properties for Live Cell Optical Imaging

Abstract

In this work, Cd-free, oleophilic (Cu)ZnInS(core)ÀZnS(shell) core/shell quantum dots (QDs) with varying Cu content in the core and shell thickness were synthesized by heating-up method (core) followed by hot-injection route (shell). Effect of Cu ion doping (in core) and shell growth on the structural and optical properties of (Cu)ZnInSÀZnS core/shell QDs is reported. Incorporation of Cu ions causes the crystalline phase transformation of zinc blende ZnInS ternary alloy to wurtzite CuÀZnÀInÀS quaternary alloy. The (Cu)ZnInS alloyed core QDs are encapsulated with a wider bandgap ZnS shell with gradient interface. The photoluminescence of (Cu)ZnInS core QDs exhibits wide tunable multicolor emissions from green (535 nm) to deep red (683 nm) with large Stokes shift. After the growth of ZnS layer, the PL peak position and absorption edge undergo a hypsochromic shift with enhanced photoluminescence quantum yield up to 47.31%, which is due to the partial cation exchange of Cu + and In 3 + with Zn 2 + , yielding a graded core/shell structure with smooth potential interface. The radiative excited state lifetime is lengthened from 22.91 ns to 291.11 ns. The mercaptoundecanoic acid (MUA) functionalized QDs have been successfully used for in vitro fluorescence cellular imaging of HEK-293 and HeLa cells. These QDs are cell permeable and suitable for visible light induced multicolor fluorescence-based cellular imaging.[a] J.

Ag-Doped ZnInS/ZnS Core/Shell Quantum Dots for Display Applications

“…On the other hand, the quenching in PL intensity of the core/shell QDs might be attributed to the lattice mismatch accompanied by the generation of defect states in QDs that become prominent when a thick semiconductor shell like ZnS encapsulated the core QDs. 9 Termination of QDs with a sulfur-rich shell and generation of midgap surface states provide effective nonradiative recombination pathways to quench the fluorescence emission, as shown in the literature. 79 The broadened profile of the PL emission can be a result of donor−acceptor pair (DAP) recombination caused by composition inhomogeneity.…”

“…This characteristic profile is partially caused by the irregular elemental distribution in the QDs, which is consistent with the properties of alloy NCs. 9 In Figure 3, it is interesting to observe that the absorption onset in the core/shell QDs is progressively shifted to a lower wavelength compared to their own core QDs while keeping the shape of the absorption spectra intact. This prominent blue shift in the absorption of the core QDs with the introduction of each shell layer growth for all of the Ag concentrations is shown in the Supporting Information (Figure S4).…”

“…The crystal planes are assigned by comparing the d values of the Ag:ZIS phase with that of the known standard ZB-ZnS structure. 9 It is to be noted that the SAED patterns contain both strong diffraction spots and diffused rings; the former characterizes the highly crystalline nature of the QDs, whereas the rings appeared due to so many QDs being kept in the field of view while acquiring the SAED pattern. At the same time, the diffusive nature of the diffraction rings signifies the nanostructured size of the QDs.…”

“…This result signifies that the composition tunability is typically controlled by cation exchange near the surface of the core QDs. 9 For a given host composition of the QDs, their emission can be well tuned across the visible spectrum by varying the dopant concentration. The emission of these core/shell QDs has been effectively tailored from 392 to 501 nm by varying the Ag content in the core QDs.…”

“…A similar trend of the PL lifetime on the dopant concentration and shell thickness has been previously reported in the literature. 9 We compared the lifetimes of various organic dyes that are used as fluorescent labels with those of the QDs in this work, and the conclusion is that the fluorophore-specific decay behavior of Ag:ZIS/ZS QDs is much higher (tunable to 403.64 and 504.72 ns) than that of the short-lived fluorescence lifetime of organic dyes such as Cynamine5 and Nile Red that have a lifetime of about 5 ns in the visible spectrum. 80 We also evaluated the CIE chromaticity diagram for one of the lowest and highest doped core/shell QDs having 0.02 and 0.1 mmol of Ag, respectively, and the CIE diagrams are presented in Figure 8.…”