A Tb ³⁺ -Based Hybrid Rare-Earth Double Perovskite with Ferroelastic Switching and Long Photoluminescence Lifetime

In recent years, hybrid rare-earth double perovskites (HREDPs) have garnered interest, owing to their significant optical properties. However, we will combine optical properties and other physical properties to promote the functional diversity of materials, so we report the successful synthesis of an HREDP, (HQ) 4 KTb(NO 3 ) 8 ( 1, HQ = quinuclidine cation), and investigate the structure–property relationships underlying its multifunctional characteristics. Differential scanning calorimetry (DSC) reveals two pairs of characteristic peaks at 262/288 K upon heating and at 254/282 K upon cooling. Dielectric measurements revealed three distinct dielectric states across the temperature range, affirming the phase-transition behavior. The reversible emergence of ferroelastic domains observed via polarized light microscopy further corroborated these transitions. Furthermore, 1 exhibits bright green emission characteristic of Tb 3+, a long fluorescence lifetime, and a photoluminescence quantum yield (PLQY) of 5.0%. This work demonstrates the successful integration of ferroelasticity and long luminescence in a single material, offering a promising platform for the development of multimodal thermal-optical responsive devices.