Lifting Triplet State Degeneracy through Organic Cation Driven Structural Perturbation to Modulate Luminescence of Sb3+-Doped Layered Double Perovskite

The spin-orbit coupling (SOC) and the Jahn-Teller effect (JTE) alter the orbital degeneracy in materials, leading to unique electronic, magnetic, and optical properties essential in spintronics, quantum computing, and LEDs. Here, we demonstrate the use of luminescent p-xylylenediammonium (PXA) instead of Cs+ in Cs2NaInCl6 to yield 2D Sb3+-doped (PXA)2NaInCl8 double perovskite, with a non-degenerate triplet state due to the enhanced JTE in the strong SOC regime and features two distinct emission centers. Consequently, a broadband emission from both PXA and [SbCl6]3- spanning the entire spectrum is achieved, representing a rare single-source multi-emissive 2D perovskite. We elucidate that the synergistic effect of SOC and JT coupling to the E_g and T_2g lattice modes modulate the electronic structure of [SbCl6]3- by splitting the doubly degenerate E levels of "3" T_1u^* into non-degenerate states, causing the dual emission. Our physical model, supported by DFT, explains the energy level splitting required to realize two kinds of radiative minima in the relaxed excited state.