Soft X-ray induced color-tunable long afterglow phosphors Ca9-xTb(PO4)7:xMn2+ based on Mn2+ modulation and energy transfer

In this paper, X-ray induced color-tunable long afterglow luminescent material Ca9-xTb(PO4)7:xMn2+ was synthesized by high-temperature solid state reaction. The effects of Mn2+ doping concentration on the properties of the samples were studied by XRD, SEM, fluorescence and afterglow spectra. The results showed that there was a very efficient energy transfer between Tb3+ and Mn2+ under X-ray excitation, with a transfer efficiency of up to 94.6%, which also contributed to the tunable green-red emission. With the increase of Mn2+ concentration, the green afterglow emissions of Tb3+ mainly at 546.9 nm gradually decreased and even disappeared, while the red afterglow emissions of Mn2+ at 647.3 nm gradually increases due to excellent energy transfer. When the doping concentration of Mn2+ was 0.07, the red afterglow emissions were the strongest. Furthermore, even at low-dose radiation (3 mGy), the sample still possessed excellent afterglow performance, which can persist for more than 5 h. In addition, the samples also showed excellent photostimulated luminescence properties, which can be persist for many cycles by the irradiation of 980 nm laser. The thermoluminescence results revealed that the doping Mn2+ ions can not only enhance the trap concentrations obviously but also created new deep traps with trap depth of 0.864 eV, which thus resulted in better long afterglow luminescence and photostimulated luminescence properties of Ca9Tb(PO4)7:Mn2+.