## 3 Results and Discussion  
To achieve high PL properties, the preparation of Sr\({}_{2-x}\)Eu\({}_{x}\)ZnMoO\({}_{6}\) powders forming the double-perovskite phase is very important, because crystallization of Sr\({}_{2-x}\)Eu\({}_{x}\)ZnMoO\({}_{6}\) powders influences their photoluminescence properties. Figure 1 shows the XRD patterns of our Sr\({}_{2-x}\)Eu\({}_{x}\)ZnMoO\({}_{6}\) powders as a function of the synthesizing temperature. The strong peaks occurred at around 31.9\({}^{\circ}\) for the (220) diffraction peak of the six host lattices. Those results suggest that the XRD patterns showed stable double-perovskite features regardless of the synthesizing temperature and Eu\({}^{3+}\) concentration. As Figure 1a shows, when the synthesizing temperature of the Sr\({}_{2-x}\)Eu\({}_{x}\)ZnMoO\({}_{6}\) powders was 900 \({}^{\circ}\)C and as the \(x\) value increased from 0 to 0.12, the 20 value of the (220) diffraction peak shifted from 31.85 to 31.87 and the full width at half maximum (FWHM) values for the (220) diffraction peak were in the range of 20 = 0.25\({}^{\circ}\)-0.27\({}^{\circ}\). When the synthesizing temperature was 1200 \({}^{\circ}\)C, the 20 value of the (220) diffraction peak shifted from 31.88 to 31.90, and the FWHM values for the (220) diffraction peak of the Sr\({}_{2-x}\)Eu\({}_{x}\)ZnMoO\({}_{6}\) powders were in the range of 20 = 0.19-0.20\({}^{\circ}\), as the \(x\) value of the Sr\({}_{2-x}\)Eu\({}_{x}\)ZnMoO\({}_{6}\) powders increased from 0 to 0.12. The results in Figure 1a-d show that the 20 of the (220) diffraction peak shifted to a higher value and the FWHM values for the (220) diffraction peaks of the Sr\({}_{2-x}\)Eu\({}_{x}\)ZnMoO\({}_{6}\) powders decreased as the synthesizing temperature increased. The ideal cubic double-perovskite structure (with the same space group Pm\(\overline{3}\)m (221)) can be described by a faced-centered cubic (fcc) lattice with lattice constant 2\(a\)[23]. The \(B(B^{\prime})\) ion is coordinated by the \(B^{\prime}(B)\) ion using an O ion as an intermediate in the middle, and the lengths of \(B\)-O and \(B^{\prime}\)-O are considered to be equal. After relaxation, both lattice constants and atomic positions reduce the ideal cubic structure (space group \(Fm\overline{3}m\)) to a tetragonal structure (space group \(I4/mmm\)). There are two O\({}_{1}\) atoms located on the \(z\)-axis with \(B\) and \(B^{\prime}\) atoms sitting between, and the four O\({}_{2}\) atoms are located on the \(xy\)-plane; the same as the \(B\) and \(B^{\prime}\) atoms. The angle of the \(B\)-O-\(B^{\prime}\) remains at 180\({}^{\circ}\) during structural optimization, whereas the lattice constant and bond length change. The lattice \(a\) can be calculated by using (1) the reflection peaks (011), (111), (200), and (220) from the XRD patterns in Figure 1; and (2) the closeness of the \(c/a\) ratio to the ideal value of \(\sqrt{2}\). As the synthesizing temperature was 900 \({}^{\circ}\)C, the Sr\({}_{2-x}\)Eu\({}_{x}\)ZnMoO\({}_{6}\) powders exhibited a cubic crystal structure with the cell parameters changing from \(a=b=c/\sqrt{2}=0.3968\) nm to \(a=b=c/\sqrt{2}=0.3971\) nm as the concentration of Eu\({}^{3+}\) ionsincreased from 0 to 0.12. The cell parameters for Sr\({}_{2-x}\)Eu\({}_{x}\)ZnMoO\({}_{6}\) powders synthesized at 1200 \({}^{\circ}\)C were also calculated from the XRD patterns shown in Figure 1, and the cell parameters changed from \(a=b=c/\sqrt{2}=0.3971\) nm to \(a=b=c/\sqrt{2}=0.3974\) nm as the concentration of Eu\({}^{3+}\) ions increased from 0 to 0.12. These results were in good agreement with those from the Joint Committee on Powder Diffraction Standards (JCPDS) file number 742474. As the results of the X-ray diffraction (XRD) patterns showed in Figure 1 were compared, these results indicated that the diffraction intensities of unknown phases for peaks located at around 20 = 28.44\({}^{\circ}\) and 33.09\({}^{\circ}\) increased as the concentration of Eu\({}^{3+}\) ions increased and decreased as the synthesizing temperature increased.