Structural color via layer-by-layer deposition: layered nanoparticle arrays with near-UV and visible reflectivity bands

Abstract

The same near-ultraviolet (NUV) (300–400 nm) light that facilitates photo-degradation in polymers is also a key component in animal communication, particularly in insects and birds. We developed a nature-inspired 1D photonic crystal structure that has simultaneous narrow stop bands in the NUV and visible wavelength range, resulting in a NUV reflector with tunable structural color in the visible region of the spectrum. The samples were prepared by high precision deposition of alternating stacks of SiO₂ and more densely packed TiO₂nanoparticlesvia aqueous layer-by-layer (LbL) deposition. Multilayer thin films with eleven stacks achieved up to 75% reflectance with a 50 nm bandwidth and 65% reflectance with a 100 nm bandwidth for structural colors centered at 500 nm and 690 nm, respectively. Despite UV absorbance of the TiO₂nanoparticles and the supporting glass substrate, all samples exhibited a narrow NUV stop-band centered in the 300–400 nm range with a reflectance over 65%. Upon introduction of a defect mode, we also demonstrated the creation of a narrow reflectance dip associated with a localized state in the photonic band gap. Multilayer-based structural colors with NUV reflectivity can be used as pigments that can promote prevention of photo-degradation in coatings, in addition to bird and insect repelling functionality.