Abstract
UV–Vis reflectance spectroscopy, combined with field emission scanning electron microscope (FE-SEM), was used to comparatively characterize nacre areas with milky-white and pink-violet coloration from the same Hyriopsis cumingii shell. Although the mean thicknesses of the aragonite platelets in the nacre from the pink-violet area were similar, the reflection spectra obtained from different locations within this area were not uniform. This indicated that the vivid color appearing on the inner surface of the shell was not completely derived from the one-dimensional photonic structure. We proposed that the absorption peak in the ultraviolet region was associated with carotenoids. The strength of the absorption peak increased with carotenoid concentration. The inner surface of the shell was not flat, leading to obvious frequency shifting in the reflection peak of the violet region. More importantly, our findings suggested that the vivid color of the inner surface of the shell was caused by the combined effects of organic pigment and one-dimensional photonic band. This present study advances our understanding of coloration mechanisms. Furthermore, we expect that our work may provide basis for further studies of pearl culture or quality grading and might inform further investigations of the design and synthesis of advanced functional materials for optical, biomedical, and mechanical applications.
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