September 14, 2026 -- Photonic crystals, which contain periodic nanostructures with dimensions of several hundred nanometers comparable to the wavelength of light, exhibit so-called structural colors by selectively reflecting specific wavelengths. Constructing photonic crystals from functional nanosheets, two-dimensional materials just a few nanometers thick, could enable the development of multifunctional photonic crystals that combine a wide range of properties. However, structural limitations of nanosheets have so far restricted photonic-crystal fabrication to only a handful of nanosheet materials.

A research team led by Associate Professor Koki Sano of the Faculty of Textile Science and Technology at Shinshu University has established a new strategy for functionalizing photonic crystals by decorating nanosheet surfaces with functional nanoparticles, enabling additional functionality while retaining the nanosheets' original properties. The researchers developed functional hybrid nanosheets by gradually decorating negatively charged titanium oxide nanosheets with positively charged gold nanoparticles, gold nanorods, and fluorescent silica nanoparticles. They then increased the spacing between the nanosheets to several hundred nanometers, creating multifunctional photonic crystals that combine three distinct optical mechanisms: light absorption, reflection, and emission. The team also visualized the nanosheets in three dimensions and demonstrated dynamic control over the optical properties of the resulting photonic crystals.

These findings could be applied to the development of novel colorants, inks, and next-generation materials with advanced optical properties. They may also serve as a foundational technology for the precise characterization of the structure and behavior of inorganic nanosheets.