Potassium and Rubidium Copper Halide A₂CuX₃ (A = K, Rb, X = Cl, Br) Micro- and Nanocrystals with Near Unity Quantum Yields for White Light Applications

Lead-free ternary metal halides, especially cesium copper halides, have attracted tremendous research interest in the past two years owing to their outstanding optical properties, such as long photoluminescence (PL) decay lifetimes and high photoluminescence quantum yields (PLQYs). Recently, single crystals of potassium and rubidium copper halides have shown potential use in optoelectronics, and several synthetic methods have been reported for A₂CuX₃ (A = K, Rb; X = Cl, Br) single crystals. Here, we have successfully synthesized A₂CuX₃ micro- and nanocrystals by both anti-solvent recrystallization and hot injection methods, achieving size and shape control of these materials for the first time. A₂CuX₃ micro- and nanocrystals show near-UV to deep blue emission, with emission peaks ranging from 380 to 400 nm. Emission properties included Stoke’s shifts over 100 nm, a fwhm of approximately 50 nm, a long PL lifetime, and high PLQYs, in particular for K₂CuCl₃, which shows near unity PLQYs. In addition, these materials can be used to produce white light along with previously reported CsCu₂I₃ nanocrystals. A mixed solution of K₂CuCl₃ and CsCu₂I₃ nanocrystals exhibits white light emission with a Commission Internationale de l’Éclairage (CIE) coordinate of (0.3456, 0.3304) and a color rendering index (CRI) of 75 at a color temperature of 4855 K.