Sequential thermochromic switching in zero-dimensional Cs2ZnCl4 metal halides

All-inorganic zero-dimensional (0D) metal halides are highly attractive for optoelectronic applications, but rational control over the temperature dependence of luminescence in these materials remains an unfulfilled task. This study presents an investigation of thermo-responsive luminescence in doped Cs2ZnCl4 crystals. Density functional theory calculations reveal a thermal elevation of the orbital state of the dopant ions originating from distortion of the local coordination polyhedron, leading to a blueshift of the self-trapped exciton (STE) emissions. By examining a series of Cs2ZnCl4 crystals doped with Sb3+, Te4+, Cu+, and Mn2+, we quantitatively address the polyhedral distortion and its effect on the luminescence properties. Owing to the 0D nature of the host material, we further synthesize Sb3+/Mn2+ co-doped Cs2ZnCl4 with dual emissions that display distinct luminescence responses to thermal stimuli. The advances in these optical materials enable a new tactic to construct tunable thermochromic luminescence for applications such as thermal sensing and optical encryption.