Lifting Triplet Degeneracy Through Organic-Cation Driven Structural Perturbation to Modulate Luminescence of Sb3+-Doped Double Perovskite.

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 Eg and T2g lattice modes modulate the electronic structure of [SbCl6]3- by splitting the doubly degenerate E levels of 3 T 1 u ∗ $^{3}{\mathrm{T}}_{1u}^*$ 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.