Synthesis of polycrystalline Ta₂O₅ inverse opal photonic crystal powders and their optical characterization

Polycrystalline Ta 2 O 5 inverse opal (IO) photonic crystal powders were synthesized using PMMA colloidal crystals as sacrificial templates. We prepared Ta 2 O 5 IO powders with vibrant structural colors at UV–vis wavelengths. The photonic bandgaps (PBGs) in the Ta 2 O 5 IO powders red-shifted as a function of both the macropore diameter and the refractive index of the medium filling the macropores. Owing to their polycrystalline structure, the Ta 2 O 5 IO powders exposed PBGs for various FCC facets, making investigation of their optical properties significantly more complex than Ta 2 O 5 IO thin films that preferentially expose only (111) planes as studied previously. Due to the overlap of the PBGs from different FCC facets and the defects that cause light scattering, much of the typical angle-dependent structural color observed in IO thin films was lost in the Ta 2 O 5 IO powders. This study offers new insights into the optical properties of IO powders. • Polycrystalline Ta 2 O 5 IO photonic crystal powders exhibiting strong structural color were successfully synthesized by the reduced-pressure impregnation method. • The PBG positions indicated by the Ta 2 O 5 IO powder were in strong agreement with the modified Bragg equation. • Owing to the polycrystalline characteristics, the Ta 2 O 5 IO powder exhibited PBGs (e.g. (220) and (311)) from multiple planes other than the (111) plane. • The PBG positions exhibited with Ta 2 O 5 IO powder lost their angular dependence on the angle of incidence of light due to scattering by a number of structural defects.