Tunable emission and thermal sensitivity via energy transfer from Bi³⁺ to Eu³⁺ in BaY₂Al₂Ga₂GeO₁₂

BaY2Al2Ga2GeO12 (BYAGGO):Eu3+ and BaY2Al2Ga2GeO12:0.03Bi(3+), yEu(3+) phosphors have been prepared via a high-temperature solid phase method. BYAGGO:Eu3+ has a stronger characteristic emission of Eu3+ at 592 nm attributed to magneto-dipole transitions under 245 nm excitation, indicating that Eu3+ is more inclined to occupy the central lattice of the octahedron with inverted symmetry. The lattice of Eu3+ ions expands to the asymmetric dodecahedron center in Eu3+ and Bi3+ ions co-doped in BYAGGO. The emission of BYAGGO:Bi3+ overlaps the excitation of BYAGGO:Eu3+, implying that energy transfer (ET) from Bi3+ to Eu3+ is possible. Furthermore, the fluorescence decay lifetime is the direct proof of energy transfer in BaY2Al2Ga2GeO12:0.03Bi(3+), yEu(3+). The energy transfer efficiency reaches 72% at y = 0.25. Finally, BYAGGO:0.03Bi(3+), 0.09Eu(3+) phosphor is employed for a WLED device with a color temperature of 3825 K and a color rendering index (Ra) of 88.75.