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.