mPEG-NH2-directed phase engineering of biphasic Cs3Cu2I5/CsCu2I3 copper halides for single-matrix white-light emission

Lead-free copper halides have emerged as promising self-trapped exciton (STE) emitters for broadband white-light generation, yet the direct construction of compositionally regulated single-matrix white emitters remains challenging. This study presents an mPEG-NH 2 -directed phase-engineering strategy for the one-step in situ construction of biphasic Cs 3 Cu 2 I 5 /CsCu 2 I 3 copper halides. By introducing methoxy polyethylene glycol amine into the ligand-assisted reprecipitation (LARP) process, the local coordination environment and supersaturation-driven nucleation behavior of Cs + , Cu + , and I − species are regulated, enabling the coexistence of blue-emitting Cs 3 Cu 2 I 5 and yellow-emitting CsCu 2 I 3 within one crystallization system. The amino and ether oxygen sites of mPEG-NH 2 further promote interfacial coupling with the copper halide matrix, reducing non-radiative STE deactivation and improving radiative recombination. The optimized CCI:3P sample exhibits broadband white-light emission with Commission Internationale de l’Éclairage (CIE) coordinates of (0.3236, 0.3347), a photoluminescence (PL) quantum yield of 42.8%, and a prolonged exciton lifetime. A UV-pumped WLED based on CCI:3P emits white light with a correlated color temperature of 6052 K. In addition, the biphasic material exhibits distinct water- and heat-induced luminescence changes, demonstrating stimulus-dependent optical contrast. This work provides a polymer-directed strategy for designing lead-free copper halide emitters with integrated white-light emission and responsive optical functionality.