Localized Excitonic Magnetic Polarons and Their Role in the Luminescence of Rare-Earth-Sulfur Codoped Divalent Metal Halides

In this work, BaCl₂:Eu²⁺,S^2- is employed as model system to investigate the formation and tunable evolution of localized excitonic magnetic polarons (LEMPs) in Eu-S codoped divalent metal halides, in which Eu-S bonding in BaCl₂ with Eu²⁺ 5d-f hybridization markedly enhances the band edge emission, shifting from 401 to 412 nm with rising EuS content, and the absorption band edge shifts from 3.02 to 2.85 eV, with EMP character. Moreover, EuS doped in different hosts (Ba < Sr < Ca) leads to a progressive red shift of EMP emission from 406 nm to the near-infrared region. Under high-energy laser excitation, these compounds can exhibit pronounced nonlinear emission with ASE-like behavior (<i>n</i> > 1), demonstrating the LEMP-cooperative radiative processes. This study establishes rare-earth-sulfur codoped halides as a promising materials platform for tuning luminescence through coupled spin-lattice-exciton interactions.