Lead-Free Zero-Dimensional Zn-Based Metal Halides of Highly Efficient Blue Luminescence from Self-Trapping Exciton

Recently, hybrid metal halides have received great attention in the field of solid-state lighting because of their diverse structures and excellent photoluminescence properties. In this work, we first reported two hybrid zinc-based metal halides with zero-dimensional structures, (BMPP)2ZnBr4 and (TBA)2ZnBr4, which exhibited broadband emission with large Stokes shifts. Notably, the highest photoluminescence quantum yield of 59.76% was observed. Additionally, the luminescence mechanism of metal halides was investigated by using time-resolved femtosecond transient absorption experiments. A broad excited-state absorption platform with the tendency of slowly decaying was shown in the detection range, demonstrating that after the electrons were excited to the excited state, the free excitons underwent a nonadiabatic transition to self-trapped excitons and went through a radiation recombination process to the ground state. A blue-light-emitting diode could be easily obtained by coating (BMPP)2ZnBr4 on a GaN chip, which indicated that it has good competitiveness in the application of solid-state lighting devices.