The synthesis of nanomaterials with a narrow size distribution is challenging, especially for III−V semiconductor nanoparticles (also known as quantum dots). Concerning phosphides, this issue has been largely attributed the use of overly reactive precursors. The problem is exacerbated due to the narrow range of competent reagents for III−V semiconductor syntheses. We report the use of sterically encumbered tris(triethylsilyl) phosphine and tris(tributylsilyl) phosphine for InP quantum dot (QD) synthesis among others. The hypothesis was that these reagents are less reactive than the near-ubiquitous precursor tris(trimethylsilyl) phosphine and can be used to create more homogeneous materials. It was found that the InP products' quantum yields and emission color saturation (fwhm) were improved, but not to the levels realized in CdSe QDs. Regardless, these reagents have other positive attributes; they are less pyrophoric and can be applied toward the synthesis of II−V semiconductors and organophosphorus compounds. Concerning safe practices, we demonstrate that ammonium bifluoride is an effective replacement for highly toxic HF for the post-treatment of III−V semiconductor quantum dots.
Quantum dot (QD)–organic dye couple chromophores are topical due to their applications in biology, catalysis, and energy. The maximization of energy transfer efficiency can be guided by the underlying Förster or Dexter mechanisms; however, the impact of fluorescence intermittency must also be considered. Here we demonstrate that the average ⟨t on⟩ and ⟨t off⟩ times of dye acceptors in coupled QD–dye chromophores are substantially affected by the donors’ blinking behavior. With regard to biological imaging, this effect beneficially minimizes the photobleaching of the acceptor dye. The implications for alternative energy are less encouraging as the acceptors’ capacity to store energy, using ⟨t on⟩/⟨t off⟩ as a metric, was reduced by as much as ∼95%. These detrimental effects can be mitigated by suppressing QD blinking via surface treatment. This study also demonstrates several instances of the nonconformity of QD blinking dynamics to a power law distribution, as a robust examination of the off times reveals log-normal behavior that is consistent with the Albery model.
The use of microfluidics in chemical synthesis is topical due to the potential to improve reproducibility and the ability promptly interrogate a wide range of reaction parameters, the latter of which is necessary for the training of artificial intelligence (AI) algorithms. Applying microfluidic techniques to semiconductor nanocrystals, or quantum dots (QDs), is challenging due to the need for a high-temperature nucleation event followed by particle growth at lower temperatures. Such a high-temperature gradient can be realized using complex, segmented microfluidic reactor designs, which represents an engineering approach. Here, an alternative chemical approach is demonstrated using the cluster seed method of nanoparticle synthesis in a simple microfluidic reactor system. This enables quantum dot nucleation at lower temperatures due to the presence of molecular organometallic compounds (NMe4)4[Cd10Se4(SPh)16] and (NMe4)4[Zn10Se4(SPh)16]. This integration of cluster seeding with microfluidics affords a new mechanism to tailor the reaction conditions for optimizing yields and tuning product properties.
Semiconductor nanocrystals (also known as quantum dots) have been extensively studied because of their unique optical properties which makes them promising candidates for bio imaging and bio sensing. II-VI semiconductor quantum dots are commonly used in biomedical applications because of their near unit quantum yields and narrow emission profiles. Despite these advantages, II-VI semiconductor nanocrystals contain toxic metals. As a result, III-V semiconductor nanocrystals such as InP are promising replacements for cadmium-based semiconductor nanocrystals. However, the synthesis of bright InP quantum dots with narrow size distribution is challenging mainly due to the use of overly reactive phosphorus precursors like tris(trimethylsilyl) phosphine (TMS)3P. This reagent is also highly flammable. We employed less pyrophoric sterically encumbered tris(triethylsilyl) phosphine and tris(tributylsilyl) phosphine for the synthesis and observed that quantum yield and the emission color saturation (fwhm) of InP nanocrystals are improved compared to those prepared with (TMS)3P, but not up to the levels realized with CdSe. HF treatment is often employed as a post-synthetic treatment to improve the optical properties of quantum dots. We demonstrate that ammonium bifluoride is a safer alternative to extremely hazardous HF. Ammonium bifluoride etched InP core dots were further passivated to create InP/ZnSeS core-shell quantum dots that were later water-solubilized and functionalized for biological applications. Figure 1
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