Ultraviolet-induced erasable photochromism in bilayer metal oxide films

We demonstrate that the optical transmittance of bilayer samples consisting of pyrolytically coated amorphous Mg–Sn–O and metal oxide films such as In2O3 and SnO2 decreases upon ultraviolet illumination, but can be recovered by annealing in air at ∼300 ∘C. Spectral, structural, and compositional studies suggest that this photochromic phenomenon is induced by photoelectronic excitation in the Mg–Sn–O film, electron injection into the metal oxide, which becomes negatively charged, and subsequent formation of metallic particles, which absorb and/or scatter visible light.