## 3 Results
### Y\({}_{2}\)O\({}_{3}\):Eu@MF Prepared by the Variation in pH and Solvents
Figure 2: Median particle size (D\({}_{50}\)) of Y\({}_{2}\)O\({}_{3}\):Eu\({}^{3+}\) nanosol dispersed in (**a**) ethanol and (**b**) H\({}_{2}\)O as solvent. Figure 4: FE-SEM images and inserted fluorescent pictures, of the powders exposed under UV lamp, of Y\({}_{2}\)O\({}_{3}\):Eu@MF calcined at 650 \({}^{\circ}\)C after coating at **(a)** pH 7 and **(b)** pH 8 in ethanol, **(c)** pH 7, and **(d)** pH 8 in water. Figure 3: Zeta potential curves of **(a)** mica and **(b)** Y\({}_{2}\)O\({}_{3}\):Eu\({}^{3+}\) as a function of pH. Figure 6 shows the photoluminescence (PL) spectra of the Y\({}_{2}\)O\({}_{3}\):Eu@MF red phosphor prepared by the variation in the calcination temperature at pH 7 in ethanol and pH 8 in water. The PL measurement range was 400-800 nm and the emission spectrum was fixed and measured at the center wavelength of 254 nm as it is the dominant excitation peak. The emission spectra peak appeared at 560 nm to 635 nm, and the weak peak was also observed at 710 nm. The relative transition of various emission spectra was due to the transition of \({}_{5}\)D\({}_{0}\rightarrow\tau\)F\({}_{2}\) (J = 0-4) in relation to the Eu\({}^{3+}\) ions. The most intense peak at 611 nm, depicted in Figure 6, could be identified as the transition from the splitting level of \({}_{5}\)D\({}_{0}\rightarrow\tau\)F\({}_{2}\) of the Eu\({}^{3+}\) ions [24]. As shown in Figure 6a, the emitted red light was very weak and dark. On the other hand, a bright red emission is shown in the inserted photograph in Figure 6b. As a result, the luminescent intensity of Y\({}_{2}\)O\({}_{3}\):Eu@MF, prepared with pH 8 in H\({}_{2}\)O, was higher than that of the sample prepared in ethanol. Figure 5: Powder XRD patterns of (**a**) mica flake and (**b**) Y\({}_{2}\)O\({}_{3}\):Eu@MF (10 wt%). Figure 6: Photoluminescence spectra of Y\({}_{2}\)O\({}_{3}\):Eu@mica red phosphor calcined at 650 \({}^{\circ}\)C after coating at (**a**) pH 7 in ethanol, and (**b**) at pH 8 in water. (Y_{2}\)O\({}_{3}\):Eu@MF Prepared by Varying Coating Amount of \(Y_{2}\)O\({}_{3}\):Eu\({}^{3+}\) and Temperatures  
The Y\({}_{2}\)O\({}_{3}\):Eu@MF was finally prepared and optimized by varying the loading amount of Y\({}_{2}\)O\({}_{3}\):Eu\({}^{3+}\), stirring temperature, and calcination temperature. Figure 7 shows the FE-SEM images of Y\({}_{2}\)O\({}_{3}\):Eu@MF prepared by 5, 10, and 20 wt% coatings of Y\({}_{2}\)O\({}_{3}\):Eu\({}^{3+}\) nanoparticles on mica in water. It can be seen that the Y\({}_{2}\)O\({}_{3}\):Eu\({}^{3+}\) nanoparticles having size less than 100 nm were individually coated on the mica flake (MF, 9-45 \(\upmu\)m in size). As the coating amount of the nanoparticles was 5 wt% as shown in Figure 7a, the coating coverage of Y\({}_{2}\)O\({}_{3}\):Eu@MF was about 10-20%. The coating coverage was calculated as the ratio of the coated nanoparticles area to the mica surface by the average value after manually mapping several sample images. The coating coverage has been increased with the increasing loading amount of the nanoparticles, as shown in Figure 7b. Herein, the coating coverage of Y\({}_{2}\)O\({}_{3}\):Eu@MF (10 wt%) was about 40-50%. However, as the loading amount exceeded 10 wt%, the coating coverage of the nanoparticles on mica decreased because of the aggregation of the nanoparticles. In order to investigate the coating property and ability of the stirring and calcination temperatures, Y\({}_{2}\)O\({}_{3}\):Eu@MF was fixed and prepared at pH 8 as depicted in Figures 8 and 9. Figure 8 shows the FE-SEM images of the Y\({}_{2}\)O\({}_{3}\):Eu@MF prepared with a 20 wt% loading amount of Y\({}_{2}\)O\({}_{3}\):Eu\({}^{3+}\) at stirring temperatures of 75, 85, and 95 \({}^{\circ}\)C, respectively. As the temperature increased, it was confirmed that the Y\({}_{2}\)O\({}_{3}\):Eu\({}^{3+}\) nanoparticles are effectively coated on the surface of MF.