Tunable photoluminescence, visible-light excitation, and high quantum yield in scalable copper cluster halide emitters for optoelectronics

Abstract

Zero-dimensional copper halide phosphors have emerged as efficient, less toxic alternatives to lead-based systems. Here, we report a bromide–iodide alloyed cluster, TPA2[Cu4Br2I4], stabilized by optoelectronically inert tetrapropylammonium (TPA+), featuring strong Cu–Cu interactions, visible-light excitation (λex = 444 nm), green-yellow emission (λem = 512 nm), and a high photoluminescence quantum yield (∼95%). Temperature- and power-dependent photoluminescence studies reveal a dual emission mechanism arising from excitonic recombination in cis and trans isomers. Time-dependent DFT calculations elucidate the photoinduced electronic redistribution and structural relaxation underlying this behavior. The material is readily synthesized via mechanochemistry and processed into thin films by spin coating or aerosol-assisted chemical vapor deposition (AACVD). Its integration into polymer composites demonstrates its practical utility for lighting applications. Finally, the successful extension of the alloying strategy to other cations such as MTPP+ highlights its versatility for designing tunable copper cluster halide phosphors aimed at next-generation optoelectronic and lighting technologies.