## 3 Results and Discussion
Concerning the structural aspect, the BaZrO\({}_{3}\) compound shows a cubic perovskite-type crystal structure and its space group (Pm3m:221) contains 48 symmetry operations including inversion. The lattice constant \(a\) in the present report was calculated by using the 20 value. The presented Eu-BZO powders exhibit cubic geometry having \(a=0.41923\) nm, which is in good agreement with Joint Committee on Powder Diffraction Standards (JCPDS) file No. 89-2486. The radii of Zr\({}^{4+}\), Ba\({}^{2+}\), and Eu\({}^{3+}\) are 0.72 A, 1.35 A, and 0.947 A, respectively. Due to the difference in the ion sizes between Ba\({}^{2+}\) and Zr\({}^{4+}\), the Eu\({}^{3+}\) ions are expected to be substituted for the Zr\({}^{4+}\) sites in the BaZrO\({}_{3}\) lattice. [PERSON] _et al._ had used the hydrothermal synthesis method to prepare the Eu-doped BaZrO\({}_{3}\) powders and they changed the amount of Eu\({}^{3+}\) ions from 2.0 to 8.0 mol. % based on the Zr\({}^{4+}\) ions [17]. The 20 value of the (110) diffraction peak of undoped BZO powders is located at 30.21 with \(a=0.41915\) nm (not shown here). If the Eu\({}^{3+}\) ions are substituted for the Ba\({}^{2+}\) sites, the lattice in the BaZrO\({}_{3}\) will decrease and the 20 value of the (110) diffraction peak will be shifted to a larger value. The 20 value of the (110) diffraction peak of the Eu-BZO powders was located at 30.18 with \(a=0.41923\) nm, which is longer than that of the undoped-BZO powders. This result suggests that Eu\({}^{3+}\) ions are substituted for the Zr\({}^{4+}\) sites and the lattice in the BaZrO\({}_{3}\) increases and the 20 value of the (110) diffraction peak will be shifted to a smaller value. Nevertheless, we used the solid-state  
Figure 2: X-ray diffraction (XRD) patterns of BaZrO\({}_{3}\):Eu\({}_{0.025}\) powders as a function of heating process and heating temperature. (**a**) One-step Eu-BZO powder and (**b**) Two-step Eu-BZO powder, respectively. reaction to prepare the 0.0125 Eu\({}_{2}\)O\({}_{3}\)-doped BaZrO\({}_{3}\), and we believe that the all Eu\({}^{3+}\) ions will occupy the Zr\({}^{4+}\) sites. The PL emission spectra of Eu-BZO powders excited at a wavelength of 271 nm are shown in Figures 3 and 4 for the light wavelength range of 450-800 nm and 550-700 nm, respectively. For the one-step and the two-step Eu-BZO powders, four emission peaks were revealed in the spectra. In the past, the spectra of BaZr\({}_{1-x}\)Eu\({}_{x}\)O\({}_{3}\) (BaZrO\({}_{3}\) doped with Eu\({}^{3+}\)) powders consisted of a series of resolved emission peaks at 574, 596, 616, 623, 651, 673, 696 and 704 nm, which can be assigned to \({}^{5}\)D\({}_{0}\)-\({}^{7}\)F\({}_{1}\) (J = 0, 1, 2, 3, 4) transitions of Eu\({}^{3+}\) ions, namely, \({}^{5}\)D\({}_{0}\)-\({}^{7}\)F\({}_{0}\) (576 nm), \({}^{5}\)D\({}_{0}\)-\({}^{7}\)F\({}_{1}\) (597 nm), \({}^{5}\)D\({}_{0}\)-\({}^{7}\)F\({}_{2}\) (616, 623 nm), \({}^{5}\)D\({}_{0}\)-\({}^{7}\)F\({}_{3}\) (651 nm), and \({}^{5}\)D\({}_{0}\)-\({}^{7}\)F\({}_{4}\) (673, 696 and 704 nm), respectively [19]. [PERSON] and [PERSON]'s research results also showed that the emission intensities of \({}^{5}\)D\({}_{0}\)-\({}^{7}\)F\({}_{0}\) (576 nm), \({}^{5}\)D\({}_{0}\)-\({}^{7}\)F\({}_{1}\) (597 nm), and \({}^{5}\)D\({}_{0}\)-\({}^{7}\)F\({}_{2}\) (616, 623 nm) almost had the same values, even if the Eu concentration in the BaZr\({}_{1-x}\)Eu\({}_{x}\)O\({}_{3}\) phosphor powders was different [19]. In this study, we had different results as compared with [PERSON] and [PERSON]'s research results. As Figures 3 and 4 show, the heated BaZrO\({}_{3}\) powders had two strong orange emission bands peaking at the wavelengths of 574 and 596 nm and two weak emission bands peaking at 620 and 650 nm under the optimum excitation optical wavelength of 271 nm.