Abstract
All‐inorganic metal halides such as Cs4PbX6 and CsPbX3 (X = Cl, Br, and I) are attracting global attention owing to their promise in optoelectronic applications. However, the presence of the toxic heavy metal lead (Pb) in these materials is a major concern. Here, a family of nontoxic high‐efficiency blue‐emitting all‐inorganic halides Rb2CuX3 (X = Br and Cl) is reported; the compounds exhibit 1D crystal structures featuring anionic 1∞[𝐶𝑢𝑋3]2− ribbons separated by Rb+ cations. The measured record high photoluminescence quantum yield values range from 64% to 100% for Rb2CuBr3 and Rb2CuCl3, respectively. Furthermore, the measured emission linewidths are quite narrow with full width at half maximum values of 54 and 52 nm for Rb2CuBr3 and Rb2CuCl3, respectively. Single crystals of Rb2CuCl3 demonstrate an anti‐Stokes photoluminescence signal, shown for the first time for Pb‐free metal halides. The discovery of highly efficient narrow blue emitters based on a nontoxic and inexpensive metal copper paves a way for the consideration of low‐cost and environmentally friendly copper halides for practical applications.