Boosting Photoluminescence of Rare‐Earth‐Based Double Perovskites by Isoelectronic Doping of ns2 Metal Ions

Abstract Doping of ns 2 metal ions as an energy transfer (ET) bridge can significantly elevate the photoluminescence properties. Nonetheless, the fundamental influence of ns 2 metal ions on the local lattice structures remains unclear, hindering the advancement of functional materials. Herein, Sb 3+ doped rare earth double perovskites is employed as a typical case to demonstrate this issue. It is found that the isoelectronic doping of Sb 3+ ions not only enhances the ET efficiency but also changes their localized electronic and lattice structures. Both density functional theory (DFT) and Judd–Ofelt (J–O) theory calculations provide unambiguous evidence that the isoelectronic doping of Sb 3+ ions enables a more localized charge density in the [LnCl 6 ] 3− (Ln: Lanthanide) octahedron and reduces the symmetry of the environment around the Ln 3+ , facilitating the radiative transition rates of Ln 3+ while enhancing their ET efficiency. Compared with Cs 2 NaScCl 6 :Ln 3+ , the ET efficiency of Cs 2 NaScCl 6 :Sb 3+ /Ln 3+ is enhanced by 1.5‐fold, reaching up to 98.3%. To the best of available knowledge, this work is the first to unravel the intrinsic mechanism of enhanced ET process enabled by isoelectronic doping via DFT and J–O theory. This research sheds light on understanding the mechanism of photophysics and rational design of the functional perovskite materials.