Facile Synthesis of High‐Quality, Water‐Soluble, Near‐Infrared‐Emitting PbS Quantum Dots

Abstract

PbS quantum dots (QDs) with strong near-infrared (NIR) fluorescence have been prepared directly in aqueous solution, by using dihydrolipoic acid (DHLA) as a stabilizer. The photoluminescence (PL) emission maximum could be tuned conveniently over a wide range (from ca. 870 nm to 1010 nm) by manipulating the experimental conditions, such as the Pb/ S or DHLA/Pb molar ratios. Under optimized conditions, the maximum PL quantum yield was approximately 10 %. These resultant PbS QDs were highly stable when stored in the dark at 4°C. After one month of storage, the PL emission intensity decreased by only about 20 %, and no obvious spectral redshift was observed. We scaled up further the synthesis of PbS QDs in the lab, where the concentration of QDs was increased to 8 mM from the usual 1 mM. The experimental

Two‐Phase Approach to High‐Quality, Oil‐Soluble, Near‐Infrared‐Emitting PbS Quantum Dots by Using Various Water‐Soluble Anion Precursors

“…Clearly, the photoemission bandwidth is narrow, with full width at halfmaximum (fwhm) on the order of approximately 100 nm. Here, it is worth noting that this fwhm value is small and comparable to the best values obtained with other synthesis routes, [19,[21][22][23][24][25][26][27] which suggests a narrow size distribution achieved without any post-synthesis size-selective precipitation ( Figure 7Ͻxigr7ϾA). Also, the PL quantum yield (QY) of the resulting oil-soluble PbS QDs in n-decane was estimated to be approximately 30 % (relative to the NIR dye cypate in 20 % aq.…”

“…10 %). [21][22][23] In addition to these advantages, the present two-phase approach is more facile and environmentally friendly, because of the use of the low-cost, less noxious, and highly reactive water-soluble Na 2 S as sulfur precursor, relative to the existing organic routes based on bis(trimethylsilyl) sulfide [(TMS) 2 S, sulfur source]. [19,24,27] As we know, the chemical (TMS) 2 S is dangerous, toxic, and expensive.…”

“…[19,[21][22][23][24][25][26][27] As expected, if we can combine the respective advantages of both approaches properly, for instance, to synthesize oil-soluble QDs by using water-soluble anion precursors, the synthesis steps of the traditional organic-phase methods will be simplified greatly. However, this has proved to be a difficulty.…”

“…10 %), although these water-soluble approaches are very facile. [21][22][23] For non-water-soluble (or oil-soluble) PbS QDs, [19] the hotinjection approach developed by Hines and Scholes seems to be the best to engineer high-quality QD ensembles. This hot-injection method was conducted by heating a mixture of lead oxide (PbO) and oleic acid (OA, as capping ligands) in octadecene (ODE) at 150°C under Ar for one hour followed by the injection of a solution of (TMS) 2 S (sulfur source) in ODE at 150°C.…”

“…In previous reports, most of the synthesis efforts have been made on synthesizing irregularly shaped PbS nanocrystals; [20] only a limited number of approaches have been used to form spherical PbS QDs, in aqueous or organic media. [19,[21][22][23][24][25][26] For water-soluble PbS QDs, prepared firstly by Kumacheva et al, [21] lead acetate and sodium sulfide were used as reactant sources, while thioglycerol and dithioglycerol were added as capping agents. However, as indicated in our recent report, [22] the resulting aqueous PbS QDs exhibited long-wavelength emission ranging from 1000 to 1400 nm, [21] relatively poor storage stability, and low photoluminescence (PL) quantum efficiency (ca.…”