Near-Unity Photoluminescence Quantum Yield in Blue-Emitting Cs₃Cu₂Br5–xIx (0 ≤ x ≤ 5)

Recently, interest in developing efficient, low-cost, nontoxic, and stable metal halide emitters that can be incorporated into solid-state lighting technologies has taken hold. Here we report nontoxic, stable, and highly efficient blue-light-emitting Cs 3 Cu 2 Br 5– x I x (0 ≤ x ≤ 5). Room-temperature photoluminescence measurements show bright blue emission in the 456 to 443 nm range with near-unity quantum yield for Cs 3 Cu 2 I 5 . Density functional theory calculations and power-dependent PL measurements suggest that the emission results from self-trapped excitons induced by strong charge localization within the zero-dimensional cluster structure of Cs 3 Cu 2 Br 5– x I x .