Luminescence and red long afterglow investigation of Eu3+–Sm3+ CO-doped CaWO4 phosphor

A series of Eu3+–Sm3+ co-doped CaWO4 phosphors were synthesized by the high temperature solid-state method. The crystal structure of the obtained samples was identified by XRD, and the results showed that all the phases were indexed to scheelite structure. The effect of the doping concentration of Sm3+ on the luminescent properties of the obtained products was investigated, and the optimal Sm3+ concentration was experimentally determined to 0.5%. The photoluminescence properties indicate that there is an efficient energy transfers from Sm3+ to Eu3+. The energy-transfer process between Sm3+ and Eu3+ was also given. Red long afterglow originating from the 5D0–7FJ (J=0, 1, 2, 3, 4) transitions of Eu3+ was observed after samples were excited by 254 nm, and the duration of the optimal sample can last more than 35 min in dark with naked eyes. The proposed explanation for the afterglow property was also discussed.