## 3 Results
### Y\({}_{2}\)O\({}_{3}\):Eu@MF Prepared by the Variation in pH and Solvents
Figure 7: FE-SEM images of Y\({}_{2}\)O\({}_{3}\):Eu@MF prepared by the variation in Y\({}_{2}\)O\({}_{3}\):Eu\({}^{3+}\) loading amount, (**a**) 5 wt%; (**b**) 10 wt% and (**c**) 20 wt% (fixed at pH 8 under 85 \({}^{\circ}\)C in H\({}_{2}\)O). Figure 11b shows the cross-sectional FE-SEM image of the Y\({}_{2}\)O\({}_{3}\):Eu@TMF (20 wt%) particle. The particle consists of the following three layers: the middle layer is the mica flake (MF) having about 314 nm thickness, and the TiO\({}_{2}\) layers coated on the MF have about 58 nm thickness, while the outside layers (bright part) coated on TMF are coated with Y\({}_{2}\)O\({}_{3}\) having about 162 nm thickness. For the MF or TMF information, these materials show different thicknesses (300-800 nm) depending on the observing spot. To identify the elements of coating layers, EDS mapping images of Y, Si, and Ti are shown in Figure 11b. The Si element of the mica layer and the Y element of the Y\({}_{2}\)O\({}_{3}\):Eu\({}^{3+}\) red phosphor layer  
Figure 8: FE-SEM images of Y\({}_{2}\)O\({}_{3}\):Eu@MF prepared by the variation in stirring temperature, (**a**) 75 \({}^{\circ}\)C; (**b**) 85 \({}^{\circ}\)C; and (**c**) 95 \({}^{\circ}\)C (fixed at pH 8 in H\({}_{2}\)O and Y\({}_{2}\)O\({}_{3}\):Eu\({}^{3+}\) loading amount 20 wt%). were clearly identified, as compared to Figure 11a. The Ti element of the TiO\({}_{2}\) layer coated on mica (TMF) is also clearly visible between the mica and the red phosphor layers. Therefore, it is demonstrated that the Y\({}_{2}\)O\({}_{3}\):Eu\({}^{3+}\) particles were coated on the TMF particles, as shown in Figures 11b and 12b. Figure 2:0 FE-SEM images of Y\({}_{2}\)O\({}_{3}\):Eu@MF prepared at the following calcination temperatures: (**a**) 650 \({}^{\circ}\)C, (**b**) 750 \({}^{\circ}\)C, and (**c**) 850 \({}^{\circ}\)C, with the synthetic condition in Figure 8b. Preparation of \(Y_{2}\)O\({}_{3}\):Eu@TMF by Varying Loading Amount of \(Y_{2}\)O\({}_{3}\):Eu\({}^{3+}\)  
TMF is a two-dimensional material that consists of a mica flake (MF) coated completely with TiO\({}_{2}\) nanoparticles having a high refractive index. The pearl property of TMF can be controlled by the TiO\({}_{2}\) coating layers. However, we required further experiments with Y\({}_{2}\)O\({}_{3}\):Eu\({}^{3+}\) loading amounts due to the wavelength overlaps between the UV absorption of TiO\({}_{2}\) and the excitation of Y\({}_{2}\)O\({}_{3}\):Eu\({}^{3+}\) red phosphor [25]. Figure 12 shows the FE-SEM images of the Y\({}_{2}\)O\({}_{3}\):Eu@TMF prepared by varying the Y\({}_{2}\)O\({}_{3}\):Eu\({}^{3+}\) loading amount from (a) 10, (b) 20, and (c) 30 wt%. In Figure 12a, the coating coverage of Y\({}_{2}\)O\({}_{3}\):Eu@TMF (10 wt%) was about 10-30 %. The coating coverage of Y\({}_{2}\)O\({}_{3}\):Eu@MF (20 wt%) in Figure 12b was about 60-70 %. Herein, the FE-SEM results  
Figure 2:1 Cross-section FE-SEM images and EDS mapping of Y, Si and Ti elements in (**a**) Y\({}_{2}\)O\({}_{3}\):Eu@MF (10 wt%) and (**b**) Y\({}_{2}\)O\({}_{3}\):Eu@TMF (20 wt%). Figure 2:2 Photoluminescence spectra of Y\({}_{2}\)O\({}_{3}\):Eu@MF red phosphor calcined at (**a**) 650 \({}^{\circ}\)C, (**b**) 750 \({}^{\circ}\)C, and (c) 850 \({}^{\circ}\)C in Figure 2:3  
confirm that the nanoparticles are effectively coated. However, the coating coverage was rapidly decreased at the 30 wt% loading amount of Y\({}_{2}\)O\({}_{3}\):Eu\({}^{3+}\) nanoparticles, and the agglomerated nanoparticles separated from TMF were observed as shown in Figure 12c. The cohesive ability between the Y\({}_{2}\)O\({}_{3}\):Eu\({}^{3+}\) nanoparticles are superior than that between the nanoparticles and TMF over 20 wt% loading. Figure 2:4 FE-SEM images and inserted fluorescent pictures, of the powders exposed under UV lamp, of Y\({}_{2}\)O\({}_{3}\):Eu@TMF prepared by the variation in Y\({}_{2}\)O\({}_{3}\):Eu\({}^{3+}\) loading amount (**a**) 10 wt%, (**b**) 20 wt%, and (**c**) 30 wt% (fixed at pH 8 and 85 \({}^{\circ}\)C in H\({}_{2}\)O).