X-ray-activated super long persistent ultraviolet A luminescence from Ca₃(PO₄)₂: Ce³⁺

In this paper, X-ray-activated super long persistent ultraviolet A luminescence from Ca-3(PO4)(2): Ce3+ has been observed. The crystal structure analysis has shown that the as-prepared samples are pure beta-Ca-3(PO4)(2) phases with rhombohedral structure and R3c space group. The photoluminescent spectra of the samples all consist of a broad band in 340-400 nm UVA1 region, which is assigned to the 5d(1)-4f(1) electronic transition of Ce3+ ions. More important, under the 3 min X-ray irradiation, Ca-3(PO4)(2): Ce3+ show super long persistent luminescence in the UVA1 region, which can persist for more than 16 h. And its afterglow intensity after 16 h decay is still 4.10 times stronger of the back ground intensity. Furthermore, only 10 s X-ray irradiation can induce excellent long persistent UVA luminescence of Ca-3(PO4)(2): 0.08Ce(3+), which can persist for more than 5 h and afterglow emission intensity is about 3.03 times of the background intensity. The trap analysis has confirmed that the different X-ray irradiation time do not create new traps and there is the same trap with 0.75 eV trap depth existing even under the extremely low X-ray dose (10 s X-ray irradiation). Furthermore, under 10 s X-ray irradiation, the thermoluminescence (TL) intensity of Ca-3(PO4)(2): 0.08Ce(3+) still reaches 0.32 times of the initial TL intensity even after 120 min, which thus leads to the super long persistent luminescence. Thus, the large amounts of trapped electrons induced by the high energy X-ray irradiation are the principal cause for super long persistent UVA luminescence of Ca-3(PO4)(2): Ce3+.