Enhanced afterglow properties in reddish-orange Ca2SnO4:Sm3+ phosphors by NH4Cl or CaCl2 flux

Abstract

Red long persistent phosphors are the key to achieving full-spectrum afterglow luminescence. However, their low initial brightness and short afterglow time are currently urgent problems to be solved. In this study, the reddish-orange long persistent phosphor Ca2SnO4:Sm3+ was successfully prepared via the high-temperature solid-state reaction method using NH4Cl and CaCl2 as the flux, respectively. It was proved that CaCl2 lowered the decomposition temperature of CaCO3 and form a liquid phase, accelerating the formation of the Ca2SnO4 phase. The afterglow time of Ca2SnO4:Sm3+ with 5 wt% NH4Cl or 5 wt% CaCl2 was respectively 12 or 24 times longer than that without any flux. 5 wt% CaCl2 addition exhibited the longest afterglow time, lasting over 83 min. It concluded that CaCl2 induced the increase in shallow trap concentration was the main reason for extending afterglow time. In addition, a phosphorescent mechanism model was proposed that the electron trap (Sm. Ca) and the hole trap (V″ Ca) played a crucial role in the energy storage of Ca2SnO4:Sm3+. Ca2SnO4:Sm3+ as a red long persistent phosphor has the potential to make full-spectrum afterglow luminescence a reality.