Excitation‐Dependent Anti‐Thermal Quenching in Zero‐Dimensional Manganese Bromides for Photoluminescence and X‐Ray Scintillation

Abstract One of the most significant challenges of luminescent materials is the thermal quenching (TQ) at high temperature. Understanding the correlation between crystal structure variation and photoluminescence (PL) quenching is significant to achieve anti‐thermal quenching (anti‐TQ) phosphors. Herein, we unveil a universal principle governing switchable TQ and anti‐TQ behaviors in zero‐dimensional (0D) organic–inorganic hybrid manganese bromides. We observed an abnormal anti‐TQ phenomenon when phosphor is excited in the valley of PL excitation (PLE) spectrum (indirect excitation) while TQ phenomenon is observed when excited in the peak and shoulder positions of PLE. Our findings demonstrate that PL intensity is influenced by two variable parameters: the effective Mn‐ligand distance and the shortest Mn−Mn distance. These excitation‐dependent TQ and anti‐TQ behaviors originate from the relative changes in these distances, which modulate the competition between radiative and nonradiative recombination rates, as evidenced at the molecular level by molecular dynamics simulation. X‐ray activated radioluminescence (RL) also exhibits anti‐TQ behavior, which is analogous to the indirect excitation of PL evolution when excited at PLE valley. These insights bridge the gap between PL and RL properties in 0D manganese halides and offer potential avenues for developing advanced anti‐TQ phosphors, efficient LEDs, and high‐performance scintillators.