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

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 Cs3Cu2X5 (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 Cs3Cu2Br5 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 K2SiF6:Mn4+. 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.

Ion Migration in Perovskite Light‐Emitting Diodes: Mechanism, Characterizations, and Material and Device Engineering

“…Most recently, stable inorganic lead-free perovskites (e.g., CsEuBr 3 , Cs 3 Cu 2 X 5 , and Cs 3 Sb 2 X 9 ) have been designed for the fabrication of durable blue PeLEDs. [267][268][269][270][271] In particular, bivalent lanthanide ions have similar ionic radius to that of Pb 2+ and possess superior luminescence properties. The emission of lanthanide and actinide compounds can range from deep blue to infrared; thus, a series of novel perovskites remain to be developed for use in stable PeLEDs.…”

Real-Time Observation of Anion-Exchange Reaction in Cs3Cu2Cl5 Single Crystal

“…Concurrently, the monoexponential decay curve provided additional evidence of such high PL QY (Figure c). The long lifetime of 118.5 μs, together with the large Stokes shift, signified the typical emission nature of self-trapped excitons in a soft halide lattice. ,,, To date, Cs 3 Cu 2 Cl 5 has been mostly prepared in powder form by solid state reactions, except for few single-crystal works via a hazardous organic-solvent route. − In the present work, high-quality Cs 3 Cu 2 Cl 5 single crystals were grown in a user-friendly aqueous solution. It was also worth noting that CuCl 2 was used in this work as a raw material, which was reduced to CuCl in the presence of H 3 PO 2 .…”

“…Thanks to the localized nature of self-trapped excitons (STE), high PL QY has been reported in many forms of Cs 3 Cu 2 Cl 5 , including nanocrystals, powders, and even thin films. In contrast, the single crystal of Cs 3 Cu 2 Cl 5 has remained scarce. ,− …”

Highly Stable Tetrahydrothiophene 1-Oxide Caged Copper Bromide and Chloride Clusters with Deep-Red to Near-IR Emission

“…The blue emission observed in heated CCB-THTO powders is different from the reported green emissive CsCu 2 Br 3 and nonemissive CsCu 2 Br 3 ,27,28 which may be caused by the distinct morphologies of materials. Although Cs 3 Cu 2 Br 5 possesses blue emission,7,9 there were no significant signals from Cs 3 Cu 2 Br 5 or CuBr in the XRD pattern of blue-emissive powders. The PLQY of the blue-emissive powders is 1.9%.…”