Size and Crystal Structure Dependence of Photochromism of Nanocrystalline WO 3 and MoO 3 Prepared by Acid-Precipitation Method

[摘要] Nanocrystallne WO3 and MoO3 with several different sizes and crystal structures were prepared by simple acidprecipitation and subsequent heat treatment. The photochromic (PC) properties of these samples were comparatively investigated in powder state by monitoring diffuse reflectance spectral changes after bandgap irradiation. The PC effect of hexagonal WO3 and monoclinic WO3 strongly depended upon crystallite size rather than crystal structure. The smaller the crystallitesize, the better the PC effect. However, orthorhombic WO·H2O and MoO3 having hexagonal and orthorhombic structures didnot follow this trend. One consistent result for all WO3 and MoO3 samples is that the heat treatment in air, which changescrystallinity, whether it changes the crystal structure or only the crystallite size, reduces the PC effect. Since the thermal treatment reduces the surface oxygen defect sites, we believe that the PC effect of WO3 and MoO3 depends critically on the surface oxygen defect sites that serve as deep trap sites for photogenerated electrons and oxygen radical holes. We also found thatthe proton insertion claimed by double charge injection model is not critical for the PC effect.

[学科分类] 化学（综合）

[关键词] Photochromism;Nanocrystalline WO3;MoO3;Double charge injection;Colorization efficiency