Polarization-Dependent Structural Colors in ZnS Nanosphere-Based Photonic Crystals for Anticounterfeiting Applications

In addition to the factors described in Bragg's law, such as lattice constraints, effective refractive indices, and reflection angles, the polarization of incident light can also affect the structural colors produced by photonic crystals (PCs). However, the reported polarization dependence of PCs is limited to reflectivity anisotropy. Here, polarization-dependent reflection wavelength anisotropy is demonstrated in PCs constructed with ZnS nanospheres (ZnS PCs). When the reflected angle is near 60° and the incident light changes from s-polarized to p-polarized, the reflection peak of ZnS PCs presents a blueshift greater than 30 nm. In particular, the wavelength difference increases with the diameter of ZnS nanospheres used to construct PCs. Such a significant wavelength shift, accompanied by simultaneous reflectivity variations, results in a significant change in the structural color of ZnS PCs. By comparing with PCs constructed with other materials, the large contrast of refractive indices between ZnS nanospheres and the air portion is proven to be the main reason for this polarization-dependent reflection wavelength anisotropy in ZnS PCs. The discovery of this property not only deepens the understanding of the properties of PCs, but further expands the potential application of PCs in anticounterfeiting, display, and other fields.