Lifting Triplet Degeneracy Through Organic-Cation Driven Structural Perturbation to Modulate Luminescence of...

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 Cs₂NaInCl₆ to yield 2D Sb³⁺-doped (PXA)₂NaInCl₈ 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 [SbCl₆]^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_2g lattice modes modulate the electronic structure of [SbCl₆]^3- by splitting the doubly degenerate E levels of ${}^3{T}_{1u}^{\ast }$ 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.