Influence of co-dopant in the europium reduction in SrAl₂O₄ host

Xerogels of strontium chlorate and aluminium chlorate doped with europium (un-co-doped) and co-doped with rare earth ions (Ln = Gd, Dy, Er and Y) were prepared using the proteic sol–gel route. Synchrotron radiation was used to investigate the effect of different co-dopants on the Eu³⁺ → Eu²⁺ reduction process during the synthesis of the samples. Samples were excited at the Eu L_III-edge and the XANES regions were analyzed. The results suggest that some of the Eu ions can be stabilized in the divalent state and that it is difficult to completely reduce Eu³⁺ to Eu²⁺ during thermal treatment. The mechanisms of the Eu reduction processes are explained by a proposed model based on the incorporation of charge-compensation defects.