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. The blue emission band at 400 nm and the yellow emission band at 550 nm are coupled to give rise to cold white emission. Theoretical calculations and spectra reveal that the photoluminescence of (DETA)InBr6 at 400 and 550 nm is attributed to free exciton and self-trapped exciton emission, respectively. It demonstrates that the nonadiabatic transition from free exciton to self-trapped exciton occurs at the ultrafast scale of <210 fs by a femtosecond transient absorption (fs-TA) measurement. The energy level of the antimony cation is located between the free exciton and the self-trapped exciton state as an "intermediate state". When doping Sb3+, energy barriers are decreased and the nonradiative recombination process is suppressed, leading to an increase in the photoluminescence quantum yields (PLQY) from 1.40% to 24.12% for (DETA)InBr6:1.5%Sb3+. In addition, the energy level of Sb3+ can facilitate the nonadiabatic transition to a self-trapped exciton, and the free exciton emission disappeared, which results in the transformation from white to yellow emission with 585 nm. These findings not only shed light on the mechanism of indium-based halide perovskite enhanced photoluminescence via an antimony(III) cation, but pave the way for the application of a simple method of mixing organic–inorganic metal halides in solid-state lighting.