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

Separation of Metallic and Semiconducting Single-Wall Carbon Nanotubes Using Sodium Hyodeoxycholate Surfactant

Although gel chromatography has demonstrated excellent structural separation ability with semiconducting single-wall carbon nanotubes (SWCNTs), structural separation of metallic SWCNTs remains a challenge due to their weak interactions with dextran-based gel media. In this work, we report a cholate derivative, sodium hyodeoxycholate (SHC), and apply it to the separation of metallic and semiconducting SWCNTs. The results demonstrate that the adsorbability of metallic SWCNTs coated by SHC and SDS surfactants on dextran-based gel can be dynamically enhanced through the addition of NaOH, and the difference in the adsorption order between metallic and semiconducting SWCNTs remains sufficiently large for their separation. In the absence of SHC, the separation efficiency and purity of metallic SWCNTs are dramatically reduced. On the basis of SHC-based mixed surfactants, diameter-controllable separation is achieved for both metallic and semiconducting SWCNTs ranging in diameter from 1.2 to 1.8 nm. The high-purity metallic SWCNTs obtained exhibit lower baseline absorption and a higher Raman radial breathing mode to G-band intensity ratio compared with that obtained by the conventional method, which is contributed by the effective removal of amorphous carbon and nanotube bundles. This work provides an effective strategy for single chirality and enantiomeric separation of metallic SWCNTs