Color-tunable phosphor of Sr₃YNa(PO₄)₃F:Tb³⁺ via interionic cross-relaxation energy transfer

A series of color-tunable Sr₃YNa(PO₄)₃F:Tb³⁺ phosphors with a fluorapatite structure were synthesized by a traditional high-temperature solid state reaction. The emitting color tuning from blue to green can be observed by gradually increasing Tb³⁺ concentrations, which is attributed to the enhanced cross-relaxation (CR) between Tb³⁺ ions, as described by (⁵D₃, ⁷F₆)-(⁵D₄, ⁷F₀). The CR process is analyzed based on the Dexter and Inokuti-Hirayama model, which is assigned to the electric dipole-dipole interaction. The energy transfer critical distance between Tb³⁺ ions is evaluated to be 18.1 Å. In addition, the thermal quenching mechanism of Sr₃YNa(PO₄)₃F:Tb³⁺ is also investigated. At the general working temperature of an LED (423 K), the luminescence intensity still maintains 81% and 92% with the Tb³⁺ concentration of 10 and 30 mol%, respectively, indicating an excellent thermal quenching performance of Tb³⁺. Due to the good optical and thermal properties, the Sr₃YNa(PO₄)₃F:Tb³⁺ phosphor can be used as a promising green emitting phosphor candidate in the field of white light applications.