Rapid Synthesis of Bright, Shape‐Controlled, Large Single Crystals of Cs3Cu2X5 for Phase Pure Single (X = Br, Cl) and Mixed Halides (X = Br/Cl) as the Blue and Green Components for Printable White Light‐Emitting Devices. Issue 20 (26th September 2021) - Zhou, Zhicong
Abstract: Ternary copper halides have garnered significant interest for their bright, high quantum yield emission stemming from the radiative decay of self‐trapped excitons (STEs). Cesium copper halides have shown promise for use in optoelectronics, including light‐emitting devices (LEDs) for lighting and displays. To date several synthetic procedures for Cs3 Cu2 X5 (X = Cl, Br, and mixed Br/Cl) have been proposed for making nanocrystals, microcrystals, or polycrystalline thin films. Here, a synthetic method for making large single crystals (SCs) with millimeter dimensions in less than 30 min is presented. Phase pure mixed halide SCs are also produced and in‐depth structural analysis has been performed for the first time, definitively showing the site preferences for mixing chloride into the pure Cs3 Cu2 Br5 structure. Quantum yields for SCs of X = Cl and Br are 100% and 27% respectively, with long lifetimes and strong evidence of STE emission. This synthesis can be used to produce white light UV‐downconversion LEDs using ternary copper halides as the blue and green components along with the commercial red phosphor K2 SiF6 :Mn 4+ . These devices give a Commission Internationale de l'Éclairage (CIE) coordinate of (0.3327, 0.3342) and color rendering index of 90% at a color temperature of ≈5500 K. Abstract : Cs3 Cu2 X5 (X = Cl, Br, mixed Br/Cl) single crystals (SCs) are synthesized by a rapid solution cooling method for the first time. Emission from these SCs can be adjusted from blue to green by tuning the halide composition. These SCs can be applied to white light emitting devices and emissive patterns can be in situ inkjet printed from the precursor solution.