Highly Reflective and Transparent Shell-Index-Matched Colloidal Crystals of Core-Shell Particles for Stacked RGB Films

Colloidal photonic crystals reflect light of a certain wavelength, according to the distance between the particles. While the reflective properties are good, the transparency is often hampered by multiple incoherent scattering events. This loss of transparency is primarily due to the large size and high scattering cross section of the particles in close-packed opals, especially in the shorter visible wavelength regime. In this work, a one-step vertical deposition method was used to assemble ZnS@SiO2 core-shell particles within a silica precursor solution to create reflective films with index-matched shells, leading to high transparency. We changed the core particle size and the number of layers to optimize the reflectance and transparency of the films. For small 65 nm core particles, high reflection intensities were difficult to obtain. However, for the 174 nm core particles, incoherent scattering led to decreased transparency. Intermediate sizes were preferred. An optimal film thickness between 2 and 5 mu m was determined. If the film thickness was below 2 mu m, broad reflection peaks were observed, while thicker films led to a loss of transparency. According to this optimization, red, green, and blue films were created. Last, a stacked RGB film comprising blue, green, and red reflective layers was successfully created by three successive coassembly steps. This was possible due to the high transparency and narrow reflection peak width of each individual coating. These films may have potential as reflective displays and smart windows and in encryption.