A Blue Sr3(PO4)2·12KSrPO4:Eu2+ Phosphor with a High Quantum Efficiency and Excellent Anti-Thermal Quenching

A series of phosphors with the formula R_xM_(21–x)/2(PO₄)₇:Eu²⁺ (R = Li⁺/Na⁺/K⁺; M = Ca²⁺/Sr²⁺/Ba²⁺; x = 0–7) has here been designed and synthesized by using a traditional high-temperature solid-state method. A spectral regulation of the phosphors in different bands was then realized by changing the value of x (i.e., by changing the R/M ratio). For R = K⁺ and M = Sr²⁺, the K_xSr_(21–x)/2(PO₄)₇:Eu²⁺ phosphor realized the spectral regulation from 401 nm to 428 nm with the change of x. For x = 6, the phosphor with the simplest chemical formula was Sr₃(PO₄)₂·12KSrPO₄:Eu²⁺ (S₃P·12SKP:0.05Eu²⁺), which possessed the highest luminescent intensity and the maximum red shift value. The external quantum efficiency (EQE) and internal quantum efficiency (IQE) of the optimized S₃P·12SKP:0.05Eu²⁺ phosphor reached 71.35% and 89.39%, respectively. Remarkably, the phosphor exhibited an excellent antithermal quenching performance with a luminescent intensity that still maintained the initial intensity value at 225 °C. A series of results showed that the S₃P·12SKP:Eu²⁺ blue phosphor had excellent application potential.