A mechanism for the long-duration phosphorescence from Eu2+ ions in SrAl2O4 crystals has been studied by evaluating the energy level and the density of the traps generated by the auxiliary activators. SrAl2O4:Eu2+ crystals doped with Nd, Sm, Gd, Dy and Y have been grown by the floating zone technique. Trap depth and trap density Lire evaluated by the thermally stimulated luminescence technique. A tentative energy diagram for the traps in the crystals has been drawn based on the hole-trap model. The trap levels vary front 0.0024 to 0.78eV with the added elements. The long-duration phosphorescence is influenced strongly by the depth and the density of the traps. The traps at around Et = 0.5 eV, which are seen in Dy- and Nd-doped specimens, are responsible for the long-duration phosphorescence. (C) 2002 Elsevier Science B.V. All rights reserved.