Thermochromic Luminescence in Low-dimensional Antimony Halide for Detection of Trace Amount of Water and Anti-counterfeiting

Stimuli-responsive luminescent switching materials with multifunctional properties are highly essential for advanced photonic applications, yet achieving such capabilities in halide perovskites continues to pose a significant challenge. In this work, we explore a new water-stimuli-responsive zero-dimensional (0D) Sb-based halide of [PhPz] 2 SbCl 7 ·2H 2 O (PhPz = phenylpiperazine), which is consist of isolated [SbCl 6 ] 3- octahedra in [PhPz] 2+ cationic matrix with guest H 2 O molecules. Under UV excitation, [PhPz] 2 SbCl 7 ·2H 2 O emits intense broadband red light with maximum emission at 645 nm, and combined optical characterization and theoretical calculations confirm that this luminescence originates from self-trapped excitons (STEs). Interestingly, the free water molecules can reversibly leave and entry the crystal lattice during heating-cooling cycles accompanied by formation of dehydrated phase, which displays strong yellow emission with maximum peak at 580 nm. Therefore, reversible luminescent switching between red and yellow emission is achieved through controllable removal and adsorption process of guest H 2 O. By virtue of this reversible thermochromic switching, this halide can be used to detect trace amount of water in various organic solvents and humidity of moist air. In addition, this switchable dual emission further realizes application in anti-counterfeiting and information encryption-decryption. This work deepens the understanding of structure-property relationships and expands the application range of 0D metal halides.