We believe that, for the first time, the UV-visible optical reflectivity of nanocrystalline ceria with various particle sizes has been measured, and their optical absorption characteristics have been studied by Kramers-Kronig transformation. The wide absorption band in the 200-480-nm range consisted of two narrow bands. This wide band was designated as the charge transfer of O↓(2p)-Ce↓(4f) while both narrow bands, which overlapped in this wide band, were due to the well-known (2)↑F↓(5/2)-(2)↑F↓(7/2) spin-orbit splitting of the Ce 4f↑(1) state. With a decrease in the particle sizes of the samples, the bandwidth expanded distinctly and a red shift in the wide band was observed. On the other hand, the band gap between the narrow bands showed a remarkable increase. All of these phenomena resulted from the effects of quantum size and the interface of nanostructured materials. # 1997 Optical Society of America
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