Effects of Integrated Carbon as a Light Absorber on the Coloration of Photonic Crystal-Based Pigments

Three-dimensionally ordered macroporous (3DOM) materials prepared by colloidal crystal templating are examples of photonic crystals that can exhibit structural color. The color intensity can vary widely, from a pale, nearly white opalescence to vivid, brilliantly metallic colors. Such variations are observed even for 3DOM materials of a single nominal composition that exhibit virtually identical structural order in scanning electron micrographs and are prepared from the same colloidal crystal templates. In this study we investigate the cause of the variations in color intensity for 3DOM ZrO2 systems, considering both the role of zirconia grains in the skeleton of the photonic crystal and the presence or absence of carbonaceous components in the material. Such components act as broad spectral light absorbers and are introduced either directly in the synthesis through the precursor and the polymeric template or by postsynthesis addition and carbonization of sucrose solutions. We conclude that grain-size effects do not play a significant role but that the carbon content in 3DOM ZrO2 provides direct control over the intensity of structural color in these photonic pigment materials.