On–Off Switching of Singlet Self‐Trapped Exciton Emission Endows Antimony‐Doped Indium Halides with Excitation‐Wavelength‐Dependent Luminescence

Abstract Excitation‐wavelength‐dependent (Ex‐De) emitters are a fascinating category of luminescent materials whose emission properties vary with the wavelength of the light used for excitation. Antimony (Sb 3+ )‐doped indium (In)‐based metal halides are efficient light emitters; however, the peak fluorescence emission of most Sb 3+ ‐activated In‐halide remains independent of the excitation wavelength. Here, the study introduces a new Sb 3+ ‐doped In‐halide cluster, (BDPA) 2 InCl 5 :Sb (BDPA + = C 15 H 18 N + , benzyldimethylphenylammonium), which demonstrates efficient Ex‐De emission originating from the on–off switchable fluorescence behavior of singlet self‐trapped exciton (STE) in 5‐coordinate Sb 3+ dopant. Interestingly, when excited within the range of 240–370 nm, photoluminescence (PL) spectra of (BDPA) 2 InCl 5 :Sb show both singlet and triplet STE emission. However, under excitation wavelengths of 370 to 420 nm, the singlet STE emission is absent, resulting in a noticeable correlated color temperature change from 1700 to 3800 K. The study provides a new approach to designing color‐tunable Sb 3+ ‐based luminophores, and also presents a novel application scenario for the widely recognized Sb 3+ doping strategy.