## 3 Results and Discussion
When the \(x\) values of Sr\({}_{2-x}\)Eu\({}_{x}\)ZnMoO\({}_{6}\) phosphors were 0.10 and 0.12, the emission intensity of the \({}^{5}\)D\({}_{0}\)-\({}^{7}\)F\({}_{1}\) (597 nm) first increased, then decreased at 1100 \({}^{\circ}\)C, and then increased at 1200 \({}^{\circ}\)C. The emission intensity of the \({}^{5}\)D\({}_{0}\)-\({}^{7}\)F\({}_{2}\) (616 nm) peaks increased with the increase in synthesizing temperature. These results suggest that 1100 \({}^{\circ}\)C is an important synthesizing temperature for Sr\({}_{2-x}\)Eu\({}_{x}\)ZnMoO\({}_{6}\) phosphors because the transition of PL properties happens at this temperature, but the reasons for this are not known. The results in Figures 3 and 4 present an important result regarding Sr\({}_{2-x}\)Eu\({}_{x}\)ZnMoO\({}_{6}\) phosphors: the PL\({}_{\text{max}}\) values of the transition of the \({}^{5}\)D\({}_{0}\)-\({}^{7}\)F\({}_{1}\) (597 nm) critically increased as the synthesizing temperature increased from 900 \({}^{\circ}\)C to 1000 \({}^{\circ}\)C, then they did not apparently increase as the synthesizing temperature increased from 1000 \({}^{\circ}\)C to 1100 \({}^{\circ}\)C, as Figure 4a shows. However, for Sr\({}_{2-x}\)Eu\({}_{x}\)ZnMoO\({}_{6}\) phosphors with \(x\) = 0.04, 0.06, and 0.08, the PL\({}_{\text{max}}\) values of the transition of the \({}^{5}\)D\({}_{0}\)-\({}^{7}\)F\({}_{2}\) (616 nm) linearly increased as the synthesizing temperature increased from 900 \({}^{\circ}\)C to 1100 \({}^{\circ}\)C. For Sr\({}_{2-x}\)Eu\({}_{x}\)ZnMoO\({}_{6}\) phosphors with \(x\) = 0.10 and 0.12, the PL\({}_{\text{max}}\) values of the transition of the \({}^{5}\)D\({}_{0}\)-\({}^{7}\)F\({}_{2}\) (616 nm) linearly increased as the synthesizing temperature increased from 900 \({}^{\circ}\)C to 1200 \({}^{\circ}\)C, as Figure 4b shows. When the synthesizing temperature was 1200 \({}^{\circ}\)C, the emission intensity of the transition of \({}^{5}\)D\({}_{0}\)-\({}^{7}\)F\({}_{2}\) (616 nm) for Sr\({}_{1.9}\)Eu\({}_{0.1}\)ZnMoO\({}_{6}\) and Sr\({}_{1.88}\)Eu\({}_{0.12}\)ZnMoO\({}_{6}\) phosphors was higher than that of \({}^{5}\)D\({}_{0}\)-\({}^{7}\)F\({}_{1}\) (597 nm), as Figure 4 shows. The transitions of \({}^{5}\)D\({}_{0}\)-\({}^{7}\)F\({}_{1}\) (588 nm), \({}^{5}\)D\({}_{0}\)-\({}^{7}\)F\({}_{2}\) (612 nm), \({}^{5}\)D\({}_{0}\)-\({}^{7}\)F\({}_{3}\) (649 nm), and \({}^{5}\)D\({}_{0}\)-\({}^{7}\)F\({}_{4}\) (695 nm) for the Eu\({}^{3+}\) ions can be simultaneously observed in the emission spectrum of the Eu\({}^{3+}\), Tb\({}^{3+}\)-co-doped one-dimensional strontium germinate, full-color nano-phosphors [(24)]. However, introduction of the Eu\({}^{3+}\) ions in the Sr\({}_{2-x}\)Eu\({}_{x}\)ZnMoO\({}_{6}\) lattice results in disorder. The disorder in the structure will cause transitions in \({}^{5}\)D\({}_{0}\)-\({}^{7}\)F\({}_{2}\) and point defects in the lattice because of differences in the chemical valence  
Figure 4: Emission intensity of Sr\({}_{2-x}\)Eu\({}_{x}\)ZnMoO\({}_{6}\) phosphors as a function of synthesizing temperature. (a) Emission peak of 597 nm; and (b) emission peak of 616 nm. and in the ionic radius between Eu\({}^{3+}\) ions and Sr\({}^{2+}\) ions. The Eu\({}^{3+}\) ions could occupy either of the sites of Sr\({}^{2+}\) or the sites of Zn\({}^{2+}\) (Mo\({}^{2+}\)) in the Sr\({}_{2-x}\)Eu\({}_{x}\)ZnMoO\({}_{6}\) phosphor's double-perovskite structure. If Eu\({}^{3+}\) ions occupy a lattice site with a strict center of symmetry, the odd terms of the static crystal field vanish. This will lead to electric dipole transitions being strictly forbidden for purely electric transitions and the transitions of the \({}^{5}\)D\({}_{0}\)-\({}^{7}\)F\({}_{1}\) (597 nm) will predominantly produce the emission. The Eu\({}^{3+}\) ions could occupy either the tetrahedral sites of Sr\({}^{2+}\) or the octahedral sites of Zn\({}^{2+}\) or Mo\({}^{6+}\) in the Sr\({}_{2-x}\)Eu\({}_{x}\)ZnMoO\({}_{6}\) double-perovskite crystal structure.