Exploring the luminescence mechanism and enabling tunable emission in Sr₃YGa₂O_7.5: Bi³⁺, Eu³⁺ phosphors for advanced UV-converted white LEDs

Inorganic phosphors with tunable broadband emission hold significant applications in solid-state lighting. Herein, a series of novel Sr₃YGa₂O_7.5: Bi³⁺, Eu³⁺ (abbreviated as SYGO: Bi³⁺, Eu³⁺) phosphors with tunable optical properties were synthesized by high-temperature solid-state reaction process. The photoluminescence excitation (PLE) spectrum of Sr₃YGa₂O_7.5: Bi³⁺ ranges from 200 to 400 nm with two peaks at 280 and 331 nm, matching well with the n-UV chip based white light-emitting diodes (WLED). Under ultraviolet light excitation, a single Bi³⁺-doped Sr₃YGa₂O_7.5 phosphor exhibited five distinct luminescence peaks at 410, 510, 560, 605, and 700 nm at 10 K, which are attributed to the ³P₁→¹S₀ transition emissions of Bi³⁺ ions occupying the four Sr sites and one Y site within the Sr₃YGa₂O_7.5 host lattice. The optical tuning of the Sr₃YGa₂O_7.5: Bi³⁺ phosphor is achieved by designing the Bi³⁺→Eu³⁺ energy transfer and changing the excitation wavelength based on the selected site occupation. The Commission Internationale de l'Eclairage (CIE) coordinates and emission color of the Sr₃YGa₂O_7.5: Bi³⁺, Eu³⁺ phosphors were successfully tuned from blue via white to red. The energy transfer efficiency from Bi³⁺ to Eu³⁺ can reach as high as 89.54 %, and this energy transfer process is predominantly governed by the dipole-quadrupole interaction. In addition, the white LED device prepared by combination of SYGO: 0.02Bi³⁺, 0.03Eu³⁺ phosphors with 365 nm chip has high color rendering index (CRI) of 85.5 and low correlated color temperature of 3537 K. As the driving current increases, the white light emitting diodes (WLED) device demonstrates good color stability. Based on these findings, the synthesized SYGO: Bi³⁺, Eu³⁺ phosphors can serve as color-tunable and single-phase white phosphors with potential applications in UV-excited white LEDs.