The origin of two quenching concentrations and unusual afterglow behaviors of Ba2SnO4:Sm3+ phosphor

► We observe the effect of two quenching concentrations in Ba2SnO4:Sm3+. ► Ba2SnO4:Sm3+ shows a sharp increase of afterglow time at certain Sm3+ content. ► Both the effects are related to the occupancy sequence of two sites for doping Sm3+. ► We present a feasible interpretation for our observations.