occurred at higher temperatures of up to 900 o C. The Eu-oxide was found to be homogeneously distributed within the ca. 10 nm sized ZnO:Eu crystals building up the nano-sponges while the XRD unit cell-parameters were virtually unchanged. EXAFS and DFT modelling suggested that (EuO1.5)4-8 clusters were present inside the ZnO crystals, in excellent agreement with the experimental data. This surprising finding explained how large amount of Eu-ions can be incorporated into ZnO without much change of XRD unit cell-parameters. With such high Eu-loading there should only be less than ca. 2 nm of ZnO between the Eu-oxide clusters. The studies also indicated that the window of carbonate-free and non-phase-separated pure ZnO:Eu nano-sponges extends to even higher Eu-doping levels.