K2CuX3 (X = Cl, Br): All-Inorganic Lead-Free Blue Emitters with Near-Unity Photoluminescence Quantum Yield

Recently, copper(I) halides have been gaining increased attention as highly luminescent nontoxic alternatives to lead halide perovskites for optoelectronic applications. Here, we report preparation of blue emitting, lead free, all-inorganic halides K2CuX3 (X = Cl, Br) through five synthetic methods including traditional solid-state and solution methods. The photoluminescence (PL) emission spectra of K2CuCl3 and K2CuBr3 exhibit narrow peaks centered at 392 and 388 nm with full widths at half-maximum (fwhm) values of ∼54 nm. The visible bright blue emission is corroborated by the remarkably high photoluminescence quantum yield (PLQY) values up to ∼97%. Furthermore, radioluminescence measurements on K2CuCl3 yield a bright peak at 404 nm under irradiation with X-rays at 200 kVp and 20 mA, which is optimal for use with PMTs and Si photomultipliers, suggesting a strong potential of this family for radiation detection applications. Based on our combined experimental and computational investigations, the origin of the efficient luminescence in K2CuX3 is attributed to the high stability self-trapped excitons (STE) formed in the one-dimensional anionic ∞1[CuX3]2– chains. Advantageously, K2CuX3 demonstrate improved air- and photostability compared to the previously reported copper(I) halides. The discovery of highly efficient and high stability light emitters based on earth-abundant copper(I) halides paves the way for their potential practical applications.