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Near-Unity Photoluminescence Quantum Yield of Core-Only InP Quantum Dots via a Simple Postsynthetic InF3 Treatment
Quantum dots (QDs) are luminescent nanomaterials with size-dependent properties, high efficiency, and pure color. These properties make QDs suitable for a wide range of optoelectronic applications, such as displays, solar cells, and bioimaging. InP QDs are considered as the next generation of QDs because they comply with EU safety regulations. Until now, the efficiency of InP QDs without additional capping material has not been high enough to meet application requirements. With our developed treatment using InF3, we reach near unity efficiency for InP QDs. The treatment is applicable to InP from different sizes and made via different synthesis methods making it valuable for all kinds of applications. Maarten Stam, Guilherme Almeida, Reinout F. Ubbink, Lara M. van der Poll, Yan B. Vogel, Hua Chen, Luca Giordano, Pieter Schiettecatte, Zeger Hens and Arjan J. Houtepen Abstract Indium phosphide (InP) quantum dots (QDs) are considered the most promising alternative for Cd and Pb-based QDs for lighting and display applications. However, while core-only QDs of CdSe and CdTe have been prepared with near-unity photoluminescence quantum yield (PLQY), this is not yet achieved for InP QDs. Treatments with HF have been used to boost the PLQY of InP core-only QDs up to 85%. However, HF etches the QDs, causing loss of material and broadening of the optical features. Here, we present a simple postsynthesis HF-free treatment that is based on passivating the surface of the InP QDs with InF3. For optimized conditions, this results in a PLQY as high as 93% and nearly monoexponential photoluminescence decay. Etching of the particle surface is entirely avoided if the treatment is performed under stringent acid-free conditions. We show that this treatment is applicable to InP QDs with various sizes and InP QDs obtained via different synthesis routes. The optical properties of the resulting core-only InP QDs are on par with InP/ZnSe/ZnS core–shell QDs, with significantly higher absorption coefficients in the blue, and with potential for faster charge transport. These are important advantages when considering InP QDs for use in micro-LEDs or photodetectors. Maarten Stam Arjan Houtepen Read the publication here
A phase inversion strategy enables thicker NMC811 electrodes for high-energy density Li-ion batteries.
Increasing the electrode thickness, thereby reducing the proportion of inactive cell components, is one way to achieve higher-energy-density lithium-ion batteries. However, when thicker electrodes are produced using the state-of-the-art slurry casting/drying procedure, this results in higher electronic and ionic overpotentials and/or mechanical failure induced by binder migration. Ethanol-induced phase inversion can effectively address these issues, as the inclusion of this processing step can produce robust, thick battery electrodes with improved electrochemical performance. These electrodes achieve higher available storage capacity per square centimeter and volume, using proven scalable technologies. Pranav Karanth, Mark Weijers, Pierfrancesco Ombrini, Davide Ripepi, Frans Ooms e Fokko M. Mulder A recent publication describing how these high capacity electrodes were obtained and tested electrochemically can be found in: A phase inversion strategy for low-tortuosity and ultrahigh-mass-loading nickel-rich layered oxide electrodes: Cell Reports Physical Science H2020 project ‘SOLIDIFY’ Within the H2020 Solidify consortium comprised of, among others, IMEC, EMPA, Fraunhofer, VDL, Umicore, and TU Delft, research was performed to arrive at high energy density solid-state lithium-metal batteries. The phase inversion-based NMC-811 cathodes that were developed by researchers at MECS/ ChemE/ TNW have been selected for the demonstrators resulting from the project, where these electrodes are infiltrated with the solid electrolyte precursor to arrive at a solid cathode composite, and then combined with a thin solid-electrolyte separator and a lithium metal anode. Pranav Karanth Mark Weijers Fokko Mulder Read the publication here
Effect of vibrational modes on fluidization characteristics and solid distribution of cohesive micro- and nano-silica powders
Fluidization of powders with small particle sizes is typically troublesome due to their cohesive nature. These powders to not transition from a packed bed into a homogeneous fluidizing one upon the introduction of a gas flow. Rather, they tend to stay mostly stationary, forming vertical channels through which the gas can escape. Several methods have been studied to overcome this behaviour and initiate fluidization, one of which is vertical vibration. We hypothesized that a horizontal component of the vibration would be more effective in disrupting the channelling, since the vibration would work perpendicular to the channel direction. In our work we compared the fluidization quality of beds of micro- and nano-particles, subjected vertical and elliptical (a combination of vertical and horizontal) vibration. In contrast to our expectations, we found that adding a horizontal component mitigated the effect of the vibrations, to the point that channels mostly remained present in the bed, whereas solely vertically vibrated beds showed full fluidization. Additionally, utilizing sectional pressure drop measurements, we showed improvements in fluidization behaviour with respect to the superficial gas velocity, which could not be acquired through conventional indicators of fluidization. Finally, we confirmed our results by X-ray imaging, where the presence or absence of channels could easily be demonstrated. Rens Kamphorst, Kaiqiao Wu, Matthijs van Baarlen, Gabrie M.H. Meesters, J. Ruud van Ommen Rens Kamphorst Go to the publication
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