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 ⁵D₀–⁷F_J (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.