Tunable Broadband Red-To-Near-Infrared Emission in Eu ²⁺ -Activated Sr _{1– <i>x</i>} Ba _<i>x</i> La ₂ Sc ₂ O ₇ Phosphors via Site-Selective Occupation and Cation Substitution

In this work, a series of Eu²⁺-doped SrLa₂Sc₂O₇ phosphors were rationally designed and synthesized, exhibiting high photoluminescence quantum yields and excellent thermal stability. Under 440 nm blue-light excitation, these phosphors show a broad red emission band centered at 613 nm, with a full width at half-maximum (fwhm) of 81 nm (corresponding to ∼0.26 eV at ∼613 nm). By employing a Sr²⁺/Ba²⁺ substitution strategy to modulate the local crystal field around Eu²⁺, both a redshift in the emission peak and significant spectral broadening were achieved. Notably, complete substitution of Sr²⁺ with Ba²⁺ yielded a BaLa₂Sc_1.985O₇:0.015Eu²⁺ phosphor that exhibits a broadband near-infrared (NIR) emission peaking at 812 nm with an ultrabroad fwhm of 318 nm (corresponding to ∼0.59 eV at ∼812 nm). Moreover, aliovalent substitution of Eu²⁺ for Sc³⁺ generates oxygen-vacancy-related defect centers that act as carrier traps, extending the emission lifetime and enhancing resistance to thermal quenching in SrLa₂Sc_1.985O₇:0.015Eu²⁺. In addition, incorporation of larger Ba²⁺ ions softens the host lattice, strengthening excited-state lattice relaxation and electron-phonon coupling, thereby increasing the Stokes shift and further broadening the Eu²⁺ emission band to realize tunable broadband red-to-NIR emission in Eu²⁺-activated Sr_1-<i>x</i>Ba_<i>x</i>La₂Sc₂O₇ phosphors. These findings broaden the family of Eu²⁺-activated scandate oxide phosphors and provide a viable strategy for tuning broadband NIR emission via targeted cation substitution devices.