摘要
We have investigated the relationship between the structural color and the periodic structure in purple pearl, a material that exhibits angle-dependent yellowish-green iridescence.Surprisingly, a hierarchical hexagonal photonic crystal stracture was discovered on the pearl surface through HRSEM observation.A finite-difference time-domain calculation was performed on this structure, and also on a multilayer structure that exists beneath the surface layer.The calculations show that the nested hexagonal photonic crystal structure is actually the origin of the yellowish-green iridescence of the pearl.