A reddish orange emissive long afterglow phosphor Ca2SnO4:Sm3+ was prepared by solid-state reaction in air atmosphere and characterized by photoluminescence, long-lasting phosphoresce. The afterglow time is more than 7 h which is the longest red or reddish orange long afterglow phosphor at the present time. The phosphorescence mechanism of the long afterglow phosphor was studied by thermoluminescence and positron annihilation lifetime experiments. The defects VCa″, structure defects Sn3+ and Sn2+ may act as hole trapping centers while the defects SmCa⋅ may act as electron trapping centers, and trapping centers play an essential role for photoenergy storage in persistent phosphors.

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