Symmetry Disruption and Charge Localization: Unraveling Roles of Sb³⁺ in Enhancing Luminescence of Rare Earth Double Perovskites

Abstract Co‐doping of rare earth (RE) and ns 2 metal ions with in double perovskites shows great promise for applications in anti‐counterfeiting, display, and radiation detection. However, the intrinsic physical nature for the enhanced photoluminescence remains unclear. Herein, we use gadolinium‐based double perovskite as the model and propose an effective strategy for co‐doping RE3+ with Sb3+ ions (5s 2 ) to modulate the photoluminescence and energy transfer. The incorporation of Sb 3+ increases the absorption cross section, thereby overcoming the limitation of 4f–4f narrowband absorption transitions. Furthermore, Sb 3+ acts as a bridge for energy transfer, significantly facilitating this process. Density functional theory calculations reveal that the introduction of Sb 3+ disrupts the symmetry of the [RECl 6 ] 3– octahedra, leading to increased distortion. Additionally, the electrons in the [RECl 6 ] 3– octahedra exhibit stronger localization in the Sb 3+ /RE 3+ co‐doped system, which enhances the Cl – –RE 3+ charge transfer process, thereby increasing the radiative transition rates and resulting in a high photoluminescence quantum yield. Our research elucidates the physical essence of Sb 3+ enhanced luminescence in RE‐based perovskites from both experimental and theoretical perspectives, providing valuable insights into modulation of luminescent properties and understanding of underlying physical mechanisms in RE 3+ doped luminescent materials.