Green persistent luminescence excitable by multiple wavelengths in the CaSc2O4:Ce3+ phosphor co-doped with Mg2+

Calcium scandate (CaSc2O4), when substituted with a small amount of the activator ion Ce3+ to replace Ca2+, is a recently discovered green-emitting phosphor promising for solid-state lighting applications. The co-doping with aliovalent ions to compensate for the net positive charge, as induced by the Ce3+ dopants, is a common approach to change the defect structure and tune the performance of the phosphor, but the underlying mechanisms are unclear. Here we investigate the effect of co-doping with charge-compensating Mg2+ to substitute for Sc3+, using photoluminescence and thermoluminescence techniques. In comparison to the defect structure in Ce3+ doped CaSc2O4, the co-doping with charge-compensating Mg2+ leads to the formation of new traps. These traps are featured by activation energies in the range 0.58-0.64 eV, can be emptied at room temperature and show green long-lasting phosphorescence after excitation at 454, 340, and 254 nm, respectively. Analysis of the spectroscopic results in terms of a vacuum referred binding energy diagram allows us to reach at a plausible luminescence mechanism in {Ce3+/Ce3+Mg2+}-doped CaSc2O4.