TiO2 Film Displays Multicolor Photochromism

Photochromic materials promise applications in data storage, display technology and construction, but individual materials have offered only a monochromatic response. In the January issue of Nature Materials, a team from the University of Tokyo, Japan Science and Technology Corp., Kanagawa Academy of Science and Technology and the University of Yokohama City has reported multicolor photochromism in a TiO₂ film loaded with Ag nanoparticles.

To fabricate the film, the scientists exposed anatase powder and AgNO₃ in ethanol to 12 hours of ultraviolet radiation, spin-coated the suspension onto glass and irradiated the film again for five days. Upon illumination with monochromatic visible light, the film changed from brownish-gray to the color of the light, with the color lasting for more than 1½ days in the dark. Subsequent exposure to UV radiation returned the film to its initial state.