The XRD and IR studies indicated that the 10Eu sample had a similar doping mode as the 5Eu sample, while the 20-33Eu sponges showed differences indicating that a different doping mode was at least partially present. As mentioned above, from structural considerations, extending the (EuO1.5)4-8 oxide cluster doping model previously obtained with EXAFS, XRD and DFT for the 5Eu samples seem possible only to ca. 10-15% Eu with the higher concentration for the larger oxide clusters with eight Eu-atoms. At higher doping levels, there would not be enough ZnO to surround the Eu-oxide clusters. Therefore, a detailed study was conducted on the 20Eu sample to find out how the Eu is distributed in this sample. The 5Eu sample was studied for comparison after heating to 650 o C in similarity with the 20Eu sample. This is higher than 600 o C used in previous studies with up to 5 mol% EuO1.5 and below 700 o C, which was previously shown to be the onset temperature for Eu2O3 crystallisation. HAADF-STEM was used to distinguish europium containing phases, where the large difference in atomic number for zinc (30) and europium (63) provide good contrast. showing an even distribution of zinc, oxygen, and europium without obvious phase separation for both samples. Regional EDX spectra of doped samples, as well as EDX mapping of pure ZnO nano-sponges were provided in supplementary materials.