UVA persistent luminescent materials have potential applications in energy-saving catalysis and photodynamic therapy. However, the charging time required for existing materials is too long, which restricts their efficiency. We developed novel UVA persistent luminescent phosphors Sr9Mg1.5(PO4)7:Ce3+ and Sr9Mg1.5(PO4)7:Ce3+,A+ (A+ = Li+, Na+, K+) which can be charged rapidly by X-rays. The co-doping of Li+, Na+ and K+ can regulate trap distributions and enhance UVA persistent luminescence properties significantly. SMPO:Ce3+,A+ can exhibit ultra-long UVA persistent luminescence peaked at 377 nm. Among them, SMPO:Ce3+,K+ shows the optimal afterglow performance, and UVA persistent luminescence of SMPO:Ce3+,K+ can last for more than 16 h with only 15 s of X-ray charging. Trap information in SMPO:Ce3+,A+ was analyzed with the help of thermoluminescence spectra. It is found that Ce3+ ions doped in Sr2+ sites serve both as emitting centers and trap centers, while Li+, Na+, and K+ are introduced as trap centers. Trap depth was calculated to be 0.42-1.17 eV in SMPO:Ce3+,K+. Shallow traps are primarily responsible for the strong initial UVA persistent luminescence, while deep traps mainly contribute to the long duration time of UVA afterglow in SMPO:Ce3+,K+. Additionally, SMPO:Ce3+,K+ also shows great potential in high-temperature persistent luminescence. Finally, persistent luminescent mechanism of SMPO:Ce3+,K+ was proposed to explain the generation of persistent luminescence.