Five samples with different the Eu doping the concentrations 0, 5, 10, 20, and 33 mol% EuO1.5 in ZnO (given below as: 0Eu, 5Eu, 10Eu, 20Eu and 33Eu) heated at 600 and 650 o C for 3 minutes were investigated. From previous studies, it was found that 5Eu nano-sponges could be obtained at 200 o C, 3 min. These sponges showed XRD patterns completely assignable to h-ZnO with very minor changes in unit cell-parameters. However, TEM, XPS, TGA and IR spectroscopy showed the presence of minor amounts of organic residues which were replaced by Eu-oxo-carbonate when heating at 300 -500 o C for 3 minutes. Heating at 600 o C for 3 min. removed the carbonate and yielded a pure oxide 5Eu nano-crystalline sponge without detectable phase separation. Upon heating at 700 o C, TEM revealed a few emerging ca. 1-3 nm sized Eu2O3 crystals at the ZnO:Eu sponge surface which grew into nano-sized c-Eu2O3 at higher temperatures. With lower Eu loading, the phase separation