## 3 Results and Discussion  
FESEM (JEOL JSM-6700, Tokyo, Japan) was used to examine the morphology of the heated Eu-BZO powders as a function of heating process and heating temperature. Figure 1 shows the FESEM images of Eu-BZO powders as a function of heating process and heating temperature, which indicates that as the heating process was changed, the surface morphologies apparently changed as well. As the heating temperature was 1100 \({}^{\circ}\)C, as Figure 1a,c show that the morphologies of the one-step and two-step heated Eu-BZO powders exhibited nanoparticle assembled matrixes. Surface morphologies of the 1200 \({}^{\circ}\)C-heated Eu-BZO powders also showed the nano-particle structure particles, and they had a similar result to those of the 1100 \({}^{\circ}\)C-heated Eu-BZO powders as well as large particle sizes (not shown here). As heating temperature was raised to 1300 \({}^{\circ}\)C, as Figure 1b,d show, the morphologies of the Eu-BZO powders exhibited large-particle assembled matrixes. As the heating temperature was raised to 1400 \({}^{\circ}\)C, the morphologies of the Eu-BZO powders also exhibited large-particle assembled matrixes (not shown here). As the same heating temperature was used, the two-step heated Eu-BZO powders aggregated together to form larger particle sizes than one-step heated powders did. Although the one-step and two-step heated Eu-BZO powders had different surface morphologies, they were a cluster of crystallines as confirmed by XRD in Figure 2. Therefore, all heated Eu-BZO powders, regardless of heating process and heating temperature, showed stable cubic perovskite features. In order to achieve high photoluminescence properties, the preparation of Eu-BZO powders forming the cubic perovskite phase is very important because the crystallization of the Eu-BZO powders will influence their photoluminescence properties. As Figure 2a shows, the 20 value of the (002) diffraction peak was shifted from 30.18 to 30.14 as the heating temperature increased from 1100 \({}^{\circ}\)C to 1400 \({}^{\circ}\)C. The full width at half maximum (FWHM) values for the (110) diffraction peak of the one-step Eu-BZO powder were 0.36, 0.27, 0.22, and 0.19, as the heating temperature was 1100 \({}^{\circ}\)C, 1200 \({}^{\circ}\)C, 1300 \({}^{\circ}\)C, and 1400 \({}^{\circ}\)C; as Figure 2b shows, the 20 value of the (110) diffraction peak was located at 30.18 as the heating temperature increased from 1100 \({}^{\circ}\)C to 1400 \({}^{\circ}\)C. The FWHM values for the (110) peak of the two-step Eu-BZO powder were 0.26, 0.25, 0.19, and 0.17, as the heating temperature at the second process was 1100 \({}^{\circ}\)C, 1200 \({}^{\circ}\)C, 1300 \({}^{\circ}\)C, and 1400 \({}^{\circ}\)C, respectively. As the same heating temperature was used, the diffraction intensity of the two-step Eu-BZO powders was higher than that of the one-step Eu-BZO powders and the FWHM value of the two-step Eu-BZO powders was smaller than that of the one-step Eu-BZO powder. These results suggest that as the same heating temperatures is used, the crystallization of the two-step Eu-BZO powders is better than that of the one-step Eu-BZO powders. Figure 1: Morphology of BaZrO\({}_{3}\):Eu\({}_{0.025}\) powders as a function of heating process and heating temperature. One-step Eu-BZO powder calcined at (**a**) 1100 \({}^{\circ}\)C and (**b**) 1300 \({}^{\circ}\)C, and two-step Eu-BZO powder calcined at (**c**) 1100 \({}^{\circ}\)C and (**d**) 1300 \({}^{\circ}\)C, respectively. For the two-step and one-step Eu-BZO powders, the diffraction intensity increased and the FWHM value decreased with the increasing heating temperature. Those results also suggest that Eu-BZO powder calcined at higher temperatures has a better crystalline structure and the pre-heating temperature and calcining temperature are the two important parameters influencing the crystalline structure of the Eu-BZO powders.