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KMID : 1059520230670010033
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Journal of the Korean Chemical Society
2023 Volume.67 No. 1 p.33 ~ p.41
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Size and Crystal Structure Dependence of Photochromism of Nanocrystalline WO3 and MoO3 Prepared by Acid-Precipitation Method
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Kwak Jun-Young
Jung Young-Hee
Kim Yeong-Il
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Abstract
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Nanocrystallne WO3 and MoO3 with several different sizes and crystal structures were prepared by simple acid precipitation and subsequent heat treatment. The photochromic (PC) properties of these samples were comparatively investi- gated in powder state by monitoring diffuse reflectance spectral changes after bandgap irradiation. The PC effect of hexago- nal WO3 and monoclinic WO3 strongly depended upon crystallite size rather than crystal structure. The smaller the crystallite size, the better the PC effect. However, orthorhombic WO·H2O and MoO3 having hexagonal and orthorhombic structures did not follow this trend. One consistent result for all WO3 and MoO3 samples is that the heat treatment in air, which changes crystallinity, whether it changes the crystal structure or only the crystallite size, reduces the PC effect. Since the thermal treat- ment reduces the surface oxygen defect sites, we believe that the PC effect of WO3 and MoO3 depends critically on the sur- face oxygen defect sites that serve as deep trap sites for photogenerated electrons and oxygen radical holes. We also found that the proton insertion claimed by double charge injection model is not critical for the PC effect.
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KEYWORD
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Photochromism, Nanocrystalline WO3, MoO3, Double charge injection, Colorization efficiency
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