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.