Structure-luminescence correlations in Eu³⁺-activated Ba₂LaVO₆ and Ba₂GdVO₆ double-perovskite phosphors

Eu³⁺-activated double perovskites have attracted increasing attention as red-emitting phosphors owing to their compositional tunability and structurally versatile host lattices. In this work, Ba₂La_1-x VO₆:xEu³⁺ and Ba₂Gd_1-x VO₆:xEu³⁺ (x = 0 and 2.5-30 mol%) phosphors were synthesized via a solid-state reaction route and systematically investigated to elucidate host-dependent luminescence behavior. X-ray diffraction combined with Rietveld refinement confirmed single-phase orthorhombic Pnma symmetry for both systems, with the La-based host exhibiting a more flexible and polarizable lattice, while the Gd-based host forms a more compact and rigid framework. Distinct host-dependent microstructural features are observed by scanning electron microscopy (SEM) for the La-based and Gd-based phosphors. X-ray photoelectron spectroscopy (XPS) was further employed to verify the elemental composition and the trivalent oxidation state of Eu ions in representative high-doping compositions. Photoluminescence studies reveal pronounced differences in emission characteristics: Ba₂LaVO₆:Eu³⁺ stabilizes an abnormal near-UV-excited ⁵D₀ → ⁷F₄-dominated orange-red emission with high dopant tolerance up to 30 mol% Eu³⁺, whereas Ba₂GdVO₆:Eu³⁺ exhibits the conventional ⁵D₀ → ⁷F₂-dominated red emission with earlier concentration quenching beyond 15 mol%. Temperature-dependent photoluminescence measurements further reveal distinct thermal quenching behaviors, reflected in different quenching onsets and half-intensity temperatures (T _0.5), which are closely linked to the lattice rigidity of the two hosts. CIE analysis shows that Ba₂LaVO₆:Eu³⁺ emits orange-red light with moderate color purity due to enhanced ⁵D₀ → ⁷F₄ emission, whereas Ba₂GdVO₆:Eu³⁺ produces deeper red emission dominated by the ⁵D₀ → ⁷F₂ transition. Overall, this comparative study establishes a clear structure-rigidity-luminescence correlation in Eu³⁺-activated Ba₂MVO₆ (M = La, Gd) phosphors, providing fundamental insight into host-controlled emission tuning in double-perovskite systems.