Lifting Triplet Degeneracy Through Organic‐Cation Driven Structural Perturbation to Modulate Luminescence of Sb 3+ ‐Doped Double Perovskite

Abstract The spin‐orbit coupling (SOC) and the Jahn‐Teller effect (JTE) alter the orbital degeneracy in materials, leading to unique optical, electronic, and magnetic properties essential in spintronics, quantum computing, and light‐emitting diodes (LEDs). Here, the study employs luminescent p‐xylylenediammonium (PXA) instead of Cs + in Cs 2 NaInCl 6 to yield 2D Sb 3+ ‐doped (PXA) 2 NaInCl 8 double perovskite and demonstrates a non‐degenerate triplet state resulting from enhanced JTE in the strong SOC regime, featuring distinct emission centers. Consequently, a broadband emission from both PXA and [SbCl 6 ] 3− spans the entire spectrum (350–750 nm), representing a rare single‐source multi‐emissive 2D perovskite. With in‐depth comparative structural, temperature‐dependent photo‐physical, and theoretical studies, it is elucidated that the synergistic effect of SOC and JTE on the E g and T 2 g lattice modes modulate the electronic structure of [SbCl 6 ] 3− by splitting the doubly degenerate E levels of into non‐degenerate states. The physical model, supported by theoretical studies, explains the energy level splitting required to realize two kinds of radiative minima in the relaxed excited state.