Narrow-Band Omnidirectional Structural Color 2008-01-1049

Automotive pigments consist of absorptive materials which absorb most of the wavelengths of light in the visible range (400-800 nm) except one particular range which gets reflected and seen as color. This coloring mechanism based on light absorption due to their molecular structure generally reflects a broader range of wavelength with a moderate reflectivity (50-60%). However in nature we find many magnificent colors in insects, butterflies, birds and fishes. These colors in nature are not based on the abortive pigments, but on the nanoscopic regular structures that interfere light reflected from those periodic sites. Since animals contain no solid metals, to produce metallic-like reflections they also rely on interference of light.^[1] Most common and well-known form of animal reflector is the multilayer type where alternating high and low refractive index layers are formed. Such nanostructure assembly can reflect light up to 100%. In order to use this technology for color application one need to design a narrow band omnidirectional reflector to avoid angle dependent reflectivity. In the present work we conducted theoretical simulation of multilayer stack formed by alternating high and low refractive index layers to identify the key parameters that allows control of the reflection band width and predicted structural parameters necessary for the narrow-band design.