Blue photoluminescence and long lasting phosphorescence properties of a novel chloride phosphate phosphor: Sr5(PO4)3Cl:Eu2+

A novel blue emitting long lasting phosphorescence phosphor Sr5(PO4)3Cl:Eu2+ is synthesized by solid state method at 1223 K in reducing atmosphere. The afterglow emission spectrum shows one broad band centered at 441 nm due to the 5d-4f transition of Eu2+ at six coordinated Sr(II) sites and the color coordinates are calculated to be (0.149, 0.095) which is close to the light blue region. The excitation band is in 240-430 nm and partly overlaps the solar irradiation on Earth's surface. The long lasting phosphorescence of the optimal sample doping by 0.1 mol%Eu2+ can be recorded for about 1040 s (0.32 mcd/m2). Thermoluminescence shows that there are at least three types of traps corresponding to peaks at 340 K, 382 K, 500 K, respectively. The filling and fading experiments reveal that the traps in Sr5(PO4)3Cl:Eu2+ are independent. The shallow traps (340 K) essentially contribute to the visible long lasting phosphorescence, while the deep traps (382 K and 500 K) are proved to be very stable. Thus, the Sr5(PO4)3Cl:Eu2+ material shows potential applications as not only a long lasting phosphorescence phosphor, but also an optical storage material.