Anomalous dual self-trapped excitons emission induced by Sb3+ doping in high-symmetry two-dimensional cesium cadmium chloride via local polarity

The broadband emission and long lifetimes of self-trapped excitons (STEs) have garnered significant interest. However, in highly symmetric all-inorganic halides, STEs behavior has traditionally been explained exclusively through Jahn–Teller distortions. Herein, we report an anomalous dual-STEs emission in Sb 3+ -doped Cs 2 CdCl 4 with a layered Ruddlesden–Popper phase. At room temperature, Cs 2 CdCl 4 :Sb 3+ exhibits a single green emission band centered at 514 nm, while an additional red-shifted emission band at 586 nm emerges at low temperatures (80–220 K). Integrated analysis combining temperature-dependent spectroscopy, time-resolved dynamics, and density functional theory (DFT) calculations reveals that the 514 nm band arises from Jahn–Teller distortion within the [SbCl 6 ] 3− octahedra, while the 586 nm band is stabilized by strong dipole–dipole coupling between the STEs dipole moment and localized polar environments created during solution synthesis. This work provides direct experimental and theoretical evidence that local polarity perturbations can regulate STEs emission even in highly symmetric all-inorganic halides. Furthermore, the Cs 2 CdCl 4 :Sb 3+ powders and their Cs 2 CdCl 4 :Sb 3+ @PDMS films exhibit excellent stability and device applicability, demonstrating promising potential for solid-state lighting and flexible optoelectronic applications.