Effect of tunable structural color caused by colloidal crystal

In this paper, two kinds of colloidal crystals, closely packed colloidal crystal and non-closely packed colloidal crystal, are fabricated. They are used to obtain tunable color by changing lattice distance and by changing refractive index contrast between the particles and the void among the particles. The reflective spectra of the two kinds of colloidal crystals are analyzed by Finite-difference time-domain (FDTD) method. It is concluded that the tunable color is mainly determined by the peak position and its intensity of reflective spectra. The shift of peak position is nearly linear to the expanded lattice distance even if the refractive index contrast is different. And the crystal with high refractive index contrast changes the peak position slower and has higher reflective intensity than that with low refractive index contrast. Besides, the optimal lattice distance of colloidal crystal is obtained when the crystal is used to acquire tunable color by changing the lattice distance.