Indium phosphide core/shell nanocrystals hold promise to replace heavy-metal-based emissive materials for bioimaging and optoelectronic applications. Uniformity of the shell passivation and the interfacial defects are critical for achieving improved optical properties. A combination of Fourier-transform infrared spectroscopy (FTIR) and liquid and solid-state NMR spectroscopy revealed a strong correlation between interfacial oxidation and photoluminescence of InP-based core/shell quantum dots. Using an automated sequential shell growth approach enabled efficient flow synthesis of InP/ZnSe/ZnS quantum dots, exhibiting high-quantum yields and narrow emission line widths. Feeding individual precursors into the reactor channel in a sequential fashion combined with inline reaction monitoring enabled precise control over layer-by-layer shell passivation of the core particles. Our findings suggest that an unintentional aminolytic reaction between oleylamine and carboxylates (two most commonly used starting materials for colloidal synthesis) introduces oxidative defects during the shelling process, thus limiting their optical properties.

Indium phosphide (InP) nanocrystals have emerged as a viable alternative to heavy metal-based colloidal quantum dots for optoelectronic applications. Traditionally, the presence of trace amounts of water during the synthesis of colloidal quantum dots is considered an undesired impurity because it prevents or slows down colloidal growth and alters the surface properties. Here, we report that fine-tuning the amount of trace water is the key for achieving sizefocused growth of monodisperse InP nanocrystals synthesized using aminophosphine precursors. Using solid-state and solution nuclear magnetic resonance, we investigated the role of trace amounts of water in surface oxidation and precursor conversion reactions. Molecular insights from UV−vis spectroscopy and NMR revealed a profound contrast between the growth rates of the nanocrystals upon the addition of water to the reaction system. We demonstrate that by addition of a specific amount of water, the reactivity of the phosphorous precursor can be tuned to enable a constant supply of monomer throughout the reaction. Under an optimal precursor conversion rate, a size-focused growth behavior that is rare for InP nanocrystals is observed, suggesting the presence of an artificial LaMer-like growth regime.

Colloidal semiconductor nanocrystals with tunable optical and electronic properties are opening up exciting opportunities for high-performance optoelectronics, photovoltaics, and bioimaging applications. Identifying the optimal synthesis conditions and screening of synthesis...

Despite the growing interest in quantum dots for applications ranging from bioimaging to display technologies, the reproducible and high‐quality synthesis of Cd‐free quantum dots (QDs) on a large scale remains challenging. Conventional large‐scale batch synthesis techniques are limited by slow precursor heating/cooling/mixing, poor reproducibility and low productivity. In recent years, the continuous flow synthesis of QDs using microfluidic approaches has shown promise to overcome the shortcomings of batch synthesis. However, the application of microfluidic reactors for synthesis of Cd‐free QDs exhibiting high photoluminescence quantum yield (PL QY) at high production rate remains a challenge. Here, we report a modular millifluidic reactor for the fully continuous multi‐step synthesis of InP/ZnSeS core‐shell QDs, that integrates the precise control over reaction conditions with the potential for gram‐scale production rates. We use a design of experiment approach to understand and optimize the process parameters for the synthesis, resulting in PL QY up to 67% with good reproducibility in terms of both QY and peak position (less than 5% standard deviation). Additionally, by changing the process parameters for different reaction stages (core and shell reactors), the wavelength of the InP/ZnSeS particles can be tuned to cover nearly the entire visible spectrum (480–650 nm).

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