Sb³⁺-doped (TEA)₂SnCl₆ metal halide for broadband emission and refractive index sensing

Lead-free metal halides with efficient broadband emission and multifunctional optical properties are highly desirable for next-generation optoelectronic and sensing applications. Herein, we report a Sb³⁺-doped (TEA)₂SnCl₆ zero-dimensional (0D) metal halide that exhibits highly efficient broadband emission and refractive index sensing capability. By systematically tuning the Sb³⁺ doping concentration, the photoluminescence quantum yield (PLQY) is significantly enhanced from nearly non-emissive to a maximum value of 84.4%. Temperature-dependent PL of (TEA)₂SnCl₆: 20%Sb³⁺ shows a large exciton binding energy (149.2 meV) and a significant Huang-Rhys factor (S = 11.37). The large S value indicates a pronounced Jahn-Teller distortion of the [SbCl₆]^2- octahedra and the formation of highly confined self-trapped excitons (STEs). Raman spectra demonstrate strong electron-phonon coupling, which stabilizes the STEs. First-principles density functional theory (DFT) calculations demonstrate that Sb³⁺ incorporation induces a transition from a direct to an indirect band gap and introduces localized electronic states near the valence band edge, facilitating exciton localization. Moreover, the integration of (TEA)₂SnCl₆: 20%Sb³⁺ into an optical fiber-based SPR sensor has successfully demonstrated its refractive index sensing capability, while its PL properties also show promising potential for fabrication into WLEDs. This work sheds light on the STE emission mechanism in Sb³⁺-doped (TEA)₂SnCl₆, underscoring its promise for both solid-state lighting and optical sensing.