Comparison of Sm³⁺ and Tb³⁺ dopant effects on the silica-based three-dimensional inverse opal photonic crystal coatings

Three-dimensional inverse opal photonic crystal (PC) materials have attracted a lot of attention nowadays due to their numerous innovative features. The structural color stands out with low toxic and environmentally friendly properties. In this study, it has been shown that eco-friendly and fadeless bright colors can be obtained at SiO₂ inverse opal PC coatings and controlled by Sm³⁺ or Tb³⁺ rare-earth dopants. The obtained Sm³⁺ and Tb³⁺ peaks proved that dopants entered the amorphous silica structure according to the XPS analysis. All synthesized inverse opal coatings surround the entire 3D structure with the honeycomb morphology. In addition, it was observed that Tb³⁺ doping made regularly arranged honeycomb morphology more perfect. The pseudo-photonic bandgap (pPBG) was blue-shifted by increasing the Tb³⁺ dopant ratio, while red-shifted by increasing the Sm³⁺ dopant ratio. Therefore, Sm³⁺ doping made PC coating surfaces’ blue color dominate, while Tb³⁺ doping made purple color dominate. Furthermore, Sm³⁺ doping led to the obtained color more vivid and clear with narrowed pPBG.