Temperature-dependent self-trapped exciton emission in Cu(I) doped zinc-based metal halides from well-resolved excited state structures

Zero-dimensional metal halides are of unique structures and tunable photoluminescence properties, showing great potential applications such as light-emitting diodes (LEDs) and sensing. Herein, we successfully synthesized Cu⁺ doped (MA)₂ZnCl₄ metal halides by a slow evaporation solvent method. The introduction of Cu⁺ results in sky-blue self-trapped exciton emission in (MA)₂ZnCl₄ at 486 nm at room temperature, and a photoluminescence quantum yield is as high as 54.9%. Interestingly, at low temperatures, Cu⁺-doped (MA)₂ZnCl₄ exhibits two emission peaks located at 482 and 605 nm, respectively. This temperature-dependent dual emission indicates two excited state structures that exist on the triplet excited-state potential energy surface. In addition, the temperature sensor we fitted has good performance (S_r = 1.65 %·K⁻¹), which is the first attempt in Cu⁺ doped Zn-based metal halides. Our work enriches the family of sky-blue metal halides and provides a promising strategy for building sky-blue LEDs.