Photochromism and white long-lasting persistent luminescence in Bi^3+-doped ZnGa_2O_4 ceramics

White long-lasting persistent luminescence covering the whole visible region in Bi3+-doped ZnGa2O4 ceramics is reported. The afterglow luminescence can be observed for several tens of minutes after 360 nm or 280 nm excitation. Photochromism is also observed during ultra-violet excitation. The persistent luminescence and photochromism are considered to originate from electron trapping by defect centers in the ZnGa2O4 crystals. The Bi3+-doped ZnGa2O4 ceramics are expected to be potential white-color afterglow phosphors.