# Color-Adjustable Devices Based on the Surface Plasmons Effect
## 3 Results and Discussion
In our experiment, for the isolated nanoparticles, when the geometric size increases, the gap between different periods decreases, which leads to the enhancement of the resonance of the local surface plasmon resonance in the space, the increase in the effective refractive index, and the transmission peak is red-shifted. Similarly, when the size of nanoparticles in the template increases and the space in the hole decreases, the effective refractive index in the hole increases and the transmission peak red-shift occurs. Figure 1: (**a**) Structural cross-sectional diagram of the unit structure in the \(X\)–\(Y\) plane. \(R\) represents the circle structure radius; \(h_{1}\) and \(h_{2}\) are the thickness of the Al and SiO\({}_{2}\); \(P_{x}\) and \(P_{y}\) are the periods; as follows: \(R=90\) nm; \(h_{1}=50\) nm; \(h_{2}=100\) nm; \(P_{x}=P_{y}=200\) nm. (**b**) Cross-sectional diagrams of the periodic circle structure arrays. (**c**) Different nanoparticles: Sphere, Cross, Torus, Cylinder and Cube—they are all made of aluminum. (**d**) Schematic of the template structure filled with different nanoparticles. Figure 3: Transmittances of the isolated nanoparticles. (**a**) Sphere; (**b**) Cross; (**c**) Torus; (**d**) Cylinder; (**e**) Cube. In these cases, we only removed the aluminum film and kept the other parameters unchanged. Figure 2: Transmittances of the template and different nanoparticles. (**a**) Template; (**b**) Sphere; (**c**) Cross; (**d**) Torus; (**e**) Cylinder; (**f**) Cube. So far, for the sake of better characterizing the color performance of our coloring device, we inverted the simulation-measured transmission spectrum to the CIE1931 chromaticity coordinate chart, in order to obtain the color coordinate points. Among them, the coordinate points on each CIE1931 chromaticity space map are obtained by the simulation measured transmission spectrum banding formula [34]:  
\[\text{X}=k\sum\
olimits_{\lambda\lambda}T(\lambda)I(\lambda)x^{\prime}(\lambda), \tag{1}\]  
\[\text{Y}=k\sum\
olimits_{\lambda\lambda}T(\lambda)I(\lambda)y^{\prime}(\lambda), \tag{2}\]  
\[\text{Z}=k\sum\
olimits_{\lambda\lambda}T(\lambda)I(\lambda)z^{\prime}(\lambda), \tag{3}\]  
\[\text{k}=100/\sum\
olimits_{\lambda\lambda}I(\lambda)z^{\prime}(\lambda), \tag{4}\]  
\[\text{x}=\text{X}/(\text{X}+\text{Y}+\text{Z}), \tag{5}\]  
\[\text{y}=\text{Y}/(\text{X}+\text{Y}+\text{Z}), \tag{6}\]  
where \(T(\lambda)\) is the transmission spectrum we detected; \(I(\lambda)\) is the spectrum of the incident light source (D65); and \(x^{\prime}(\lambda),y^{\prime}(\lambda)\), and \(z^{\prime}(\lambda)\) represent the tristimulus value. The wavelength ranges are 400 nm to 700 nm, which basically covers the visible light ranges. Additionally, (\(x\), \(y\)), obtained from Equations (5) and (6), are the chromaticity coordinates of the transmission spectrum. As shown in Figure 4b-f, the color display of five different nanoparticles can cover the visible light regions. The specific color distribution is shown in Figure 4a. In general, we have investigated the structure-color display via periodic subwavelength nanoparticle-hole arrays in a metal film by using FDTD software. From Figure 4d, it is apparent that when the nanoparticles choose the torus structures, the ranges of color distribution are more extensive, and the contrast between the colors presented by each parameter is also relatively clear. It is also well confirmed in the color display of Figure 4a. Therefore, in practical applications, we can  
Figure 4: **(a)** Color display of the different nanoparticles at different geometric parameters. **(b–f)** CIE1931 color space inversion map distribution under different conditions. adopt torus structure nanoparticles preferentially. In addition, when the sizes of nanoparticles with different structures are different, the saturation and intensity of color rendering effect are also different. Consequently, we can provide 30 different color renderings in the device we built, including different light intensity and saturation.