We reported the synthesis of a novel red long-afterglow material Sr(2)SnO(4):Sm(3+). Comparing with the air-sintered sample, a significant enhancement in both the fluorescence and phosphorescence for the vacuum-sintered sample was observed. This improvement could be attributed to the increase of oxygen vacancies which act as the sensitizer and the electron traps for the effective energy transfer from Sr(2)SnO(4) host to Sm(3+). The defects act as traps were investigated with thermoluminescence. For the presence of deep stable traps able to immobilize the energy permanently at room temperature, the Sr(2)SnO(4):Sm(3+) could be considered as a potential storage phosphor as well.