A Cu+-Doped Zinc Organic Halide with Temperature-Dependent Dual-color Emission as Thermochromic Molecular Thermometer

Zero-dimension (0D) zinc halides have attracted intensive attention in multiple optoelectronic fields due to their excellent stability. However, most Zn-based halides show relatively weak luminescence efficiency, which limits their further widespread applications. Herein, we successfully optimized the electronic structure of a new 0D Zn halide [MTPP]2ZnBr4 ([MTPP]Br = Methyltriphenylphosphonium bromide) by Cu+ doping strategy to realize highly efficient and adjustable dual-color emission. Compared with weak blue-green emission of undoped [MTPP]2ZnBr4, the incorporating of Cu+ ion results in a newly emerged intense orange emission at 630 nm with highest photoluminescence quantum yield (PLQY) of 39.17%. More significantly, the relative intensities of dual emission feature transformation depending on environment temperature due to thermally associated reversible energy transfer between each self-trapped excitonic (STE) state, which enables this doped phase to act as a promising luminescent ratiometric thermometer with relative thermal sensitivity of 0.94% K-1 in the range of 80-260 K. Furthermore, this phenomenon also enables the material to achieve tunable multicolor luminescence with advanced applications in anti-counterfeiting. This study not only realizes highly efficient dual-color emissions in Zn-based halide, but also achieves temperature-dependent thermochromism luminescence with wide applications in temperature monitoring and anti-counterfeiting.