Factors of Importance for Arsenic Migration/Separation under Coffee-Ring Effect on Silver Nanofilms

Surface-enhanced Raman spectroscopy (SERS) has been recognized as a promising analytical technique owing to its merit of nondestructive and fast detection capabilities. However, SERS usually suffers signal interferences from different analytes or a complicated matrix. Separation is an effective approach to solve the signal interference in the application of SERS. It was proposed that two concentric coffee rings could serve as a simple separation platform; however, there are still many questions to be answered for in-depth understanding. In this study, critical parameters during the formation of two concentric coffee rings are characterized for a better understanding of this phenomenon, including surface tension, surface morphology, and surface energy. Two arsenicals, including arsenate (AsV) and cacodylic acid (DMAV), are chosen to study the arsenicals’ separation/migration mechanism due to their significant difference in chemical properties. In the typical coffee ring, these two arsenicals have signal interference and only DMAV is detected via SERS; however, they are detected along the radius of the two concentric coffee rings. The distribution of arsenicals on the two concentric coffee rings is further verified by the chromatographic method. Under this simple platform, interactions between the arsenicals and the surface of the silver nanofilm are pivotal to their migration/separation. By surface modification of silver nanofilm with small molecules, the surface polarity and surface ζ potential are manipulated. The signal dynamics of these two arsenicals are studied on these modified silver nanofilms. It is clear that the electrostatic interaction plays a more important role than the polarity in the arsenicals’ migration. This study reveals the mechanism of small molecule migration/separation in the two concentric coffee rings and provides insights for future study of employing this simple platform

Boosting Stability and Inkjet Printability of Pure-Red CsPb(Br/I)₃ Quantum Dots through Dual-Shell Encapsulation for Micro-LED Displays

The development of pure-red perovskite quantum dots (QDs) for displays is lagging due to their structural instability. Herein, we present a new core dual-shell structure with CsPb(Br/I)3@SiO2@polystyrene (PS) QDs, emitting at 627 nm. The structure consists of a CsPb(Br/I)3 core, an intermediate SiO2 layer, and an outermost PS shell. The PS shell plays a crucial role in silane hydrolysis, preventing SiO2 aggregation and enhancing the dispersibility of the CsPb(Br/I)3@SiO2@PS QDs. These QDs exhibit enhanced resilience against irradiation, moisture, and thermal stress, maintaining approximately 80% of their initial photoluminescence (PL) intensity after 3 days of UV irradiation exposure or after 2 days of being subject to high humidity and temperature conditions. Utilized as red inkjet inks, these QDs enable the inkjet printing of a vivid red dot matrix and a Chinese chess pattern. This innovation holds promise for expanding the practical utilization of CsPb(Br/I)3 QDs, particularly in full-color micro-LED display technology via inkjet printing

Suppression of Photoinduced Phase Segregation in Mixed-Halide Perovskite Nanocrystals for Stable Light-Emitting Diodes

Halide segregation is a critical bottleneck that hampers the application of mixed-halide perovskite nanocrystals (NCs) in both electroluminescent and down-conversion red-light-emitting diodes. Herein, we report a strategy that combines precursor and surface engineering to obtain pure-red-emitting (peaked at 624 nm) NCs with a photoluminescence quantum yield of up to 92% and strongly suppresses the halide segregation of mixed-halide NCs under light irradiation. Red-light-emitting diodes (LED) using these mixed-halide NCs as phosphors exhibit color-stable emission with a negligible peak shift and spectral broadening during operation over 240 min. By contrast, a dramatic peak shift and spectral broadening were observed after 10 min of operation in LEDs based on mixed-halide NCs synthesized by a traditional method. Our strategy is critical to achieving photo- and band-gap-stable mixed-halide perovskite NCs for a variety of optoelectronic applications such as micro-LEDs