## 3 Results and Discussion
The emission spectrum consisted of sharp peaks of two strong bands at 574 and 596 nm corresponding to the \({}^{5}\)D\({}_{0}\)-\({}^{7}\)F\({}_{0}\) (574 nm) and \({}^{5}\)D\({}_{0}\)-\({}^{7}\)F\({}_{1}\) (596 nm) transitions of Eu\({}^{3+}\) ions, and of two weak bands at 620 and 650 nm corresponding to the \({}^{5}\)D\({}_{0}\)-\({}^{7}\)F\({}_{2}\) (620 nm) and \({}^{5}\)D\({}_{0}\)-\({}^{7}\)F\({}_{3}\) (650 nm) transitions of Eu\({}^{3+}\) ions, respectively. The maximum emission intensity, which will occur dependent on the heating process and heating temperature, will be observed at 574 nm or 596 nm due to the \({}^{5}\)D\({}_{0}\)\(\rightarrow\)\({}^{7}\)F\({}_{0}\) or \({}^{5}\)D\({}_{0}\)\(\rightarrow\)\({}^{7}\)F\({}_{1}\) transitions of Eu\({}^{3+}\). Figure 3: Emission spectrum of BaZrO\({}_{3}\):Eu\({}_{0,025}\) powders in the light wavelength of 450–800 nm as a function of heating process and heating temperature. (**a**) One-step Eu-BZO powders and (**b**) two-step Eu-BZO powders, respectively. (\(\lambda_{\rm em}\): main peak of excitation spectra.) As Figure 4a,b show, no matter how the one-step Eu-BZO powders or the two-step Eu-BZO powders were measured, the splitting at the peak of \({}^{5}\)D\({}_{0}\)-\({}^{7}\)F\({}_{2}\) (616, 623 nm) was not observed in the one-step Eu-BZO powders or the two-step Eu-BZO powders. Also, the \({}^{5}\)D\({}_{0}\)-\({}^{7}\)F\({}_{4}\) (673, 696, and 704 nm) peak was not observed in Figure 4a,b. The results in Figure 4 also show that with the temperature changing from 1200 \({}^{\circ}\)C to 1300 \({}^{\circ}\)C, the emission peak had large variation. For one-step Eu-BZO powders, as the heating temperature was changed from 1200 \({}^{\circ}\)C to 1300 \({}^{\circ}\)C, the emission peak with the maximum intensity would change from the transition of \({}^{5}\)D\({}_{0}\)-\({}^{7}\)F\({}_{0}\) to that of \({}^{5}\)D\({}_{0}\)-\({}^{7}\)F\({}_{1}\). For two-step Eu-BZO powders, as the heating temperature was changed from 1200 \({}^{\circ}\)C to 1300 \({}^{\circ}\)C, the emission peak with the maximum intensity would change from the transition of \({}^{5}\)D\({}_{0}\)-\({}^{7}\)F\({}_{1}\) to that of \({}^{5}\)D\({}_{0}\)-\({}^{7}\)F\({}_{0}\). The maximum emission intensities (PLmax) values of Eu-BZO powders in the transitions of the \({}^{5}\)D\({}_{0}\)-\({}^{7}\)F\({}_{0}\) (576 nm) and \({}^{5}\)D\({}_{0}\)-\({}^{7}\)F\({}_{1}\) (597 nm) peaks are presented in Figure 5 as a function of heating process and temperature. Those results suggest again that the PL characteristics of Eu-BZO powders are strongly affected by the heating process and heating temperature. The emission intensity of the \({}^{5}\)D\({}_{0}\)-\({}^{7}\)F\({}_{1}\) (576 nm) peak of one-step Eu-BZO powders and that of the \({}^{5}\)D\({}_{0}\)-\({}^{7}\)F\({}_{0}\) (597 nm) peak of two-step Eu-BZO powders increased with the rising heating temperature, and the variations in the \({}^{5}\)D\({}_{0}\)-\({}^{7}\)F\({}_{0}\) peak of one-step Eu-BZO powders and in the \({}^{5}\)D\({}_{0}\)-\({}^{7}\)F\({}_{1}\) peak of two-step Eu-BZO powders had no apparent trend with the rising heating temperature. Thus, the maximum PLmax of all BaZrO\({}_{3}\):Eu\({}_{0.025}\) phosphors occurs for particles heated at 1400 \({}^{\circ}\)C. Based on our SEM observations, we think this is the result of the Eu-BZO particle sizes increasing with rising heating temperature. Figure 4: Emission spectrum of BaZrO\({}_{3}\):Eu\({}_{0.025}\) powders in the light wavelength of 550–700 nm as a function of heating process and heating temperature. (**a**) One-step Eu-BZO powders and (**b**) Two-step Eu-BZO powders, respectively. Figure 6 shows the emission photographs of heated Eu-BZO powders heated with different processes and temperatures. Those photographs prove that Eu-BZO phosphors with very bright emission intensity can easily be obtained by heating oxide precursors.