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

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)-doped indium (In)-based metal halides are efficient light emitters; however, the peak fluorescence emission of most Sb-activated In-halide remains independent of the excitation wavelength. Here, the study introduces a new Sb-doped In-halide cluster, (BDPA)InCl:Sb (BDPA = CHN, 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 dopant. Interestingly, when excited within the range of 240-370 nm, photoluminescence (PL) spectra of (BDPA)InCl: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-based luminophores, and also presents a novel application scenario for the widely recognized Sb doping strategy.