The crucial impact of cerium reduction on photoluminescence

Abstract Rare earth-based inorganic phosphors are of great interest for solid-state lighting because some of them present very efficient luminescence properties. However, their performances strongly depend on several parameters. For multivalent dopants such as cerium, a widely used activator in the lighting industry, a synthesis in reducing atmosphere is often required to stabilize the dopant in its lower oxidation state. Surprisingly, this crucial step is not much considered, and the presence of the reduced state only is often assumed. However, the presence of the dopants oxidized form has been previously evidenced after such reductions. In this case, a question remains open about the impact of the Ce3+/Ce4+ ratio on the materials optical properties. As an example, different CaSc2O4:Ce samples were prepared and their Ce3+/Ce4+ ratios were probed by diffuse reflection and XANES. The evolution of their photoluminescence properties was investigated to rationalize the progressive reduction of dopants.