Lifting Triplet Degeneracy Through Organic‐Cation Driven Structural Perturbation to Modulate Luminescence of Sb ³⁺ ‐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 E_g and T_2g lattice modes modulate the electronic structure of [SbCl₆]^3- by splitting the doubly degenerate E levels of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics> <mml:mrow><mml:msup><mml:mrow></mml:mrow> <mml:mn>3</mml:mn></mml:msup> <mml:msubsup><mml:mi>T</mml:mi> <mml:mrow><mml:mn>1</mml:mn> <mml:mi>u</mml:mi></mml:mrow> <mml:mo>∗</mml:mo></mml:msubsup> </mml:mrow> <mml:annotation>$^{3}{\mathrm{T}}_{1u}^*$</mml:annotation></mml:semantics> </mml:math> 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.