## 3 Results and Discussion
The 20 value of the (220) diffraction peak was shifted to a higher value, as the concentration of Eu\({}^{3+}\) was equal to, or greater than, 0.02. The ion radius of Sr\({}^{2+}\) is 0.130 nm and the ion radius of Eu\({}^{3+}\) is 0.1087 nm. Hence, as more Sr\({}^{2+}\) would have been substituted by Eu\({}^{3+}\), the ionic radius of the Sr\({}_{2-x}\)Eu\({}_{x}\)ZnMoO\({}_{6}\) phosphors would have decreased, increasing the 20 value of the (220) diffraction peak. The ion radius of Eu\({}^{2+}\) is 0.131 nm, which is thought to be the same as the ion radius of Sr\({}^{2+}\). If Eu\({}_{2}\)O\({}_{3}\) exists as Eu\({}^{2+}\) ions, the cell parameters of the Sr\({}_{2-x}\)Eu\({}_{x}\)ZnMoO\({}_{6}\) phosphors would not have been changed. The shift of the (220) diffraction peak to a higher 20 value or the decrease in the cell parameters can prove that Eu\({}_{2}\)O\({}_{3}\) existed in the Sr\({}_{2-x}\)Eu\({}_{x}\)ZnMoO\({}_{6}\) phosphors and in the Eu\({}^{3+}\) state. In order to find the best doping concentration of Eu\({}^{3+}\), we synthesized a series of Sr\({}_{2-x}\)Eu\({}_{x}\)ZnMoO\({}_{6}\) phosphors (\(x\) = 0 to 0.12) and measured their emission spectra. The PL emission spectra of Sr\({}_{2-x}\)Eu\({}_{x}\)ZnMoO\({}_{6}\) powders excited at a wavelength of 350 nm are shown in Figure 3 for the light wavelength range of 400-650 nm. The spectra in Figure 3 show that that all the excitation spectra of Sr\({}_{2-x}\)Eu\({}_{x}\)ZnMoO\({}_{6}\) phosphors (except the Sr\({}_{2}\)ZnMoO\({}_{6}\) powder) consisted of two parts: one broad band in the 400-575 nm region and two sharp peaks located at 597 nm and 616 nm. However, for the Sr\({}_{2}\)ZnMoO\({}_{6}\) powder, even when the synthesizing temperature was 1200 \({}^{\circ}\)C, the two sharp peaks of Sr\({}_{2-x}\)Eu\({}_{x}\)ZnMoO\({}_{6}\) phosphors located at 597 nm and 616 nm were not found in the emission spectra. This means that no characteristic peaks were observed in Sr\({}_{2}\)ZnMoO\({}_{6}\) powder even when the synthesizing temperature was 1200 \({}^{\circ}\)C. Obviously, the broad band in the 400-575 nm region is assignable to the well-known O\({}^{2}\)-Mo\({}^{6+}\) charge transfer band (CTB) [25]. As Eu\({}_{2}\)O\({}_{3}\) was substituted for  
Figure 2: XRD patterns of Sr\({}_{2-x}\)Eu\({}_{x}\)ZnMoO\({}_{6}\) phosphors synthesized at 1200 \({}^{\circ}\)C for 4 h.  
SrO, the Sr\({}_{2-x}\)Eu\({}_{x}\)ZnMoO\({}_{6}\) phosphors had the same spectral profile, but with a different concentration of Eu\({}^{3+}\) ions, the characteristic peaks were observed. When the synthesizing temperature was changed from 900 to 1200 \({}^{\circ}\)C, the emission spectra of the Sr\({}_{2-x}\)Eu\({}_{x}\)ZnMoO\({}_{6}\) phosphors consisted of sharp peaks in two strong bands at 597 and 616 nm, corresponding to the \({}^{5}\)D\({}_{0}\)-\({}^{7}\)F\({}_{1}\) (597 nm) and \({}^{5}\)D\({}_{0}\)-\({}^{7}\)F\({}_{2}\) (616 nm) transitions of Eu\({}^{3+}\) ions. These results prove that the two emission peaks of the Sr\({}_{2-x}\)Eu\({}_{x}\)ZnMoO\({}_{6}\) phosphors, \({}^{5}\)D\({}_{0}\)-\({}^{7}\)F\({}_{1}\) at 597 nm and \({}^{5}\)D\({}_{0}\)-\({}^{7}\)F\({}_{2}\) at 616 nm, were excited by the addition of Eu\({}^{3+}\) ions. When the synthesizing temperature was raised to 1100 and 1200 \({}^{\circ}\)C, the intensity of the broadened emission went from 400 nm to 575 nm, increasing with the increase in the Eu\({}^{3+}\) ion concentration. However, the emission intensities of the Sr\({}_{2-x}\)Eu\({}_{x}\)ZnMoO\({}_{6}\) phosphors were influenced by the synthesizing temperature and the concentration of the Eu\({}^{3+}\) ions.