Thermally Reversible Luminescence in Ferroelastic Phase Transition Materials

Abstract The thermally reversible luminescent materials with information encryption are important and widely used in the information age. However, it is challenging to obtain such materials. In this work, a 0D In‐based hybrid compound [(CH 3 ) 3 NCH 2 CHCH 2 ] 2 InCl 5 ((TAMAC) 2 InCl 5 ) is synthesized and undergoes a high‐temperature ferroelastic phase transition with an Aizu notation of m mF 2/ m at 333 K. In the room temperature phase (RTP), it shows a weak blue glow with a photoluminescent quantum yield (PLQY) of 0.32% under the UV lamp at 365 nm. By using a metal ion doping strategy to improve the photophysical properties, a series of compounds is obtained: (TAMAC) 2 In 1‐ x Cl 5 : x Sb 3+ ( x = 0.1%,0.5%,1%, and 1.5%, x represents the actual amount) with the same ferroelastic phase transition as that found in (TAMAC) 2 InCl 5 . When x = 0.5%, the PLQY reaches 50.66% with the luminous color change from blue to orange. Interestingly, it is found that the orange luminescence of the doped materials can rapidly and reversibly quench and recover between heating and cooling cycles, where the thermally induced phase transition results in this thermally reversible luminescence phenomenon. This discovery reveals the mechanism of luminescence quenching and phase transition, and provides a new pathway for the construction of new thermal‐sensitive luminescent materials with information encryption.