Tunable Broadband Red-To-Near-Infrared Emission in Eu2+-Activated Sr1–xBaxLa2Sc2O7 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 BaLa2Sc1.985O7:0.015Eu2+ 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 SrLa2Sc1.985O7:0.015Eu2+. 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 Sr1–xBaxLa2Sc2O7 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.