## 3 Results  
### Y\({}_{2}\)O\({}_{3}\):Eu@MF Prepared by the Variation in pH and Solvents  
To disperse the aggregated Y\({}_{2}\)O\({}_{3}\):Eu\({}^{3+}\) nanophosphor prepared by the template method, the Y\({}_{2}\)O\({}_{3}\):Eu\({}^{3+}\) nanosol was prepared and optimized by controlling the solvents, pH, and a dispersant agent (acrylate copolymer) to improve the dispersibility under the bead-mill wet process. Figure 2 displays the particle size distribution of the Y\({}_{2}\)O\({}_{3}\):Eu\({}^{3+}\) nanosol dispersed in ethanol or water. The nanosol dispersed in ethanol, as in Figure 2a, has around 134 nm of the median particle size (D\({}_{50}\)), whereas that in water, Figure 2b, has around 120 nm [21]. Figure 1: Preparation process of Y\({}_{2}\)O\({}_{3}\):Eu\({}^{3+}\) red phosphor coated on MF or TMF. Here, the zeta potential of the Y\({}_{2}\)O\({}_{3}\):Eu\({}^{3+}\) dispersed in H\({}_{2}\)O is 40.4 mV, but 15.3 mV in ethanol. Generally, if the absolute value of the zeta potential is more than 30 mV, the dispersion stability is excellent due to the strong repulsive force between the particles [22]. It can be explained that the Y\({}_{2}\)O\({}_{3}\):Eu\({}^{3+}\) dispersed in H\({}_{2}\)O is more stable than that dispersed in ethanol. Also, H\({}_{2}\)O and ethanol are both hydrophilic. The difference of the dispersions in the two solutions is considered to be the relative polarity. While H\({}_{2}\)O has only a hydroxyl group which is hydrophilic, ethanol has a hydroxyl group and an alkyl group, which is lipophilic [23], so the difference in polarities is expected to have caused a difference in the dispersion stability. To coat Y\({}_{2}\)O\({}_{3}\):Eu\({}^{3+}\) nanoparticles on the surface of the mica flake (MF), the electrostatic attraction between the two particles was observed via the zeta potential of Y\({}_{2}\)O\({}_{3}\):Eu\({}^{3+}\) and MF. Figure 3 shows the zeta potential curves of the MF and Y\({}_{2}\)O\({}_{3}\):Eu\({}^{3+}\) particles measured in the pH range of 1-10. In the case of MF, the zeta potential tends to decrease from +30 mV to \(-\)55 mV on increasing the pH from 1 to 10. The isoelectric point (IEP) of mica is at about a pH of 5.5. Y\({}_{2}\)O\({}_{3}\):Eu\({}^{3+}\) nanoparticles modified with an acrylic copolymer have a (+) charge in the entire pH range. Therefore, the coating process between Y\({}_{2}\)O\({}_{3}\):Eu\({}^{3+}\) and mica is considered to be the most effective in the pH range of 7-9, at which the potential difference is the highest. Figure 4 displays the FE-SEM images of the Y\({}_{2}\)O\({}_{3}\):Eu@MF red phosphors prepared by varying the pH of ethanol or water. Figure 4a,b show the surface of the Y\({}_{2}\)O\({}_{3}\):Eu@MF at pH 7 and 8, respectively, in the ethanol system. It was confirmed that the coating coverage ratio of the Y\({}_{2}\)O\({}_{3}\):Eu\({}^{3+}\) particles on the surface of MF was about 5% or less. The sample prepared at pH 7 in the water system was about 1-5%, as depicted in Figure 4c. Interestingly, the sample prepared at pH 8 was coated with 30-40% coverage of Y\({}_{2}\)O\({}_{3}\):Eu\({}^{3+}\), as shown in Figure 4d. Under the condition of pH 8, the zeta potential difference between the surface charge of the (+) charged Y\({}_{2}\)O\({}_{3}\):Eu\({}^{3+}\) and the (-) charged mica was 85 mV. It means that the two particles interact more effectively and are coated to prepare Y\({}_{2}\)O\({}_{3}\):Eu@MF. Therefore, Y\({}_{2}\)O\({}_{3}\):Eu@MF was carried out at pH 8 in the water environment in order to optimize the coating ability of the Y\({}_{2}\)O\({}_{3}\):Eu\({}^{3+}\) nanoparticles. Figure 5 shows the XRD patterns of MF and Y\({}_{2}\)O\({}_{3}\):Eu@MF. MF was observed to be well crystallized, belonging to a phlogopite (JCPDS No. 16-0344) as depicted in Figure 5a,b shows that the enlarged XRD pattern of Y\({}_{2}\)O\({}_{3}\):Eu@MF (10 wt%) is matched well with the cubic structure of Y\({}_{2}\)O\({}_{3}\) (JCPDS No. 76-0151) along with a phlogopite Mica structure.