Efficient White Light Emission of 0D Lead-Free Indium-Based Halide Perovskite and the Intermediate State Promotion Mechanism of the Nonadiabatic Transition to Self-Trapped Exciton via Antimony(III) Cation Doping

In this work, we report a zero-dimensional single-component(0D)(C4H16N3)InBr6 (C4H13N3 (DETA) = diethylenetriamine),which emits white light through a simple mechanochemical method. Theblue emission band at 400 nm and the yellow emission band at 550 nmare coupled to give rise to cold white emission. Theoretical calculationsand spectra reveal that the photoluminescence of (DETA)InBr6 at 400 and 550 nm is attributed to free exciton and self-trappedexciton emission, respectively. It demonstrates that the nonadiabatictransition from free exciton to self-trapped exciton occurs at theultrafast scale of <210 fs by a femtosecond transient absorption(fs-TA) measurement. The energy level of the antimony cation is locatedbetween the free exciton and the self-trapped exciton state as an"intermediate state". When doping Sb3+, energybarriers are decreased and the nonradiative recombination processis suppressed, leading to an increase in the photoluminescence quantumyields (PLQY) from 1.40% to 24.12% for (DETA)InBr6:1.5%Sb3+. In addition, the energy level of Sb3+ can facilitatethe nonadiabatic transition to a self-trapped exciton, and the freeexciton emission disappeared, which results in the transformationfrom white to yellow emission with 585 nm. These findings not onlyshed light on the mechanism of indium-based halide perovskite enhancedphotoluminescence via an antimony(III) cation, but pave the way forthe application of a simple method of mixing organic-inorganicmetal halides in solid-state lighting.