TiO2 films loaded with silver nanoparticles:: Control of multicolor photochromic behavior

Ag-TiO2 films exhibiting multicolor photochromism were prepared by photoelectrochemical reduction of Ag+ to Ag nanoparticles in nanoporous TiO2 films under UV light. Color of the Ag-TiO2 film, initially brownish-gray, changes under a colored visible light to the color of the light and reverts to brownish-gray under UV light. Their chromogenic properties were improved by simultaneous irradiation for Ag deposition with UV and blue lights to suppress the formation of anisotropic Ag particles. Nonvolatilization of a color image was also achieved by removing Ag+ that was generated during the irradiation with a colored light. Once nonvolatilized, the image can be reproduced by UV light, even after the image is discolored under white light. This new effect evidenced that nanopores in the TiO2 film determine the resonance wavelengths of the Ag particles, as their molds. In addition, solvatochromic behavior of the Ag-TiO2 film proved that nanospaces left around the Ag nanoparticles affect the resonance wavelengths of the Ag particles.