Bright Green Emission from Self-Trapped Excitons Triggered by Sb³⁺ Doping in Rb₄CdCl₆

Sb3+ with stereochemically active lone pair 5s2 electrons is overwhelming in the doping engineering of the luminescent metal halides, and it usually leads to extrinsic self-trapped excitons (STEs) with tunable emissions. However, the photoluminescence enhancement mechanism of Sb3+ doped metal halides compared to the pristine host remains unclear. Herein, we doped Sb3+ into all-inorganic non-emissive Rb4CdCl6, realizing bright green emission peaking at 525 nm with a photoluminescence quantum yield of 70.2%. A comparison of Raman spectra, as well as the Debye temperature, was utilized to elucidate the STEs mechanism, verifying that the doping of Sb3+ softens the structural lattice. Thus, strong electron–phonon interactions enable highly efficient photoluminescence originating from STEs emission in Rb4CdCl6:Sb3+. This work demonstrates solid evidence that the efficient emissions of metal halides can be triggered by Sb3+ doping, and the design principle involved will guide the future studies for emerging luminescence material exploration.