Enhanced Luminescence and Thermal Stability in High Gd³⁺/Eu³⁺ Co-Doped Ba₃Y₄O₉ Phosphors via Co-Precipitation Method

The co-precipitation method was successfully used to synthesize Ba₃(Y_0.6-xGd_0.4Eu_x)₄O₉ (0.01 ≤ x ≤ 0.09) phosphors with heavy Gd³⁺ doping, resulting in significantly enhanced thermal stability and luminescence performance. Structural analyses confirm that Gd³⁺ and Eu³⁺ ions substitute Y³⁺ in the lattice, causing lattice expansion and improving crystal asymmetry, which enhances Eu³⁺ emission. The incorporation of Gd³⁺ creates efficient energy transfer pathways to Eu³⁺ while suppressing non-radiative relaxation, leading to stable fluorescence lifetimes even at elevated temperatures. With a thermal activation energy of ~0.3051 eV, the Ba₃(Y_0.55Gd_0.4Eu_0.05)₄O₉ phosphor exhibits superior resistance to thermal quenching compared to Ba₃(Y_0.95Eu_0.05)₄O₉ and many conventional red phosphors. Furthermore, the reduced color temperature and stable emission spectra across a wide temperature range highlight its potential for advanced lighting and display technologies in high-temperature environments.