Pure White Emission with 91.9% Photoluminescence Quantum Yield of [(C₃H₇)₄N]₂Cu₂I₄ out of Polaronic States and Ultra-High Color Rendering Index

cluster, whose populations could be scaled by temperature, together with the local dipole orientation modulation of neighboring STEs and phase transition related emission color coordinate change. Particularly, the outstanding chemical- and antiwater stability of this compound was also demonstrated. This work illustrates the potential of such cuprous halide perovskite-type materials in multifunctional applications, such as lighting in varied environments.