Controllable Synthesis of Undoped and Doped Calcium Niobate Nanocrystals for Tailored Structural, Electronic, and Luminescent Properties

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• 作者：Yiguo Su ; Liman Peng ; Chunfang Du ; Xiaojing Wang
• 刊名：The Journal of Physical Chemistry C
• 出版年：2012
• 出版时间：January 12, 2012
• 年：2012
• 卷：116
• 期：1
• 页码：15-21
• 全文大小：433K
• 年卷期：v.116,no.1(January 12, 2012)
• ISSN：1932-7455

文摘

In this work, we report on the phase and particle size control of Ca₂Nb₂O₇ nanocrystals with an aim of tailoring structural, electronic, and luminescent properties. Using citric acid as the capping agent, the as-prepared nanocrystals exhibited a phase transformation from orthorhombic CaNb₂O₆ to cubic Ca₂Nb₂O₇. The samples were carefully characterized by X-ray diffraction, transmission electron microscopy, Fourier transformed infrared spectroscopy, UV鈥搗is diffuse reflectance spectroscopy, and luminescence spectroscopy. It is found that Ca₂Nb₂O₇ showed particle sizes ranging from 14.6 to 26.9 nm by regulating the pH value under hydrothermal conditions. Contrary to the theoretical predictions of the quantum size effect, Ca₂Nb₂O₇ showed an abnormal band gap narrowing with particle size reduction, which can be well-defined as a function of lattice volumes, surface defects, and the surface dipole layer. As for the Eu³⁺-doped samples, it is shown that Eu³⁺ and K⁺ were simultaneously substituted at Ca²⁺ sites in the Ca₂Nb₂O₇ host lattice, which allows one to vary the local symmetry surrounding Eu³⁺ for an enhanced luminescence property. As the consequence of the particle size effect and variation of the local symmetry, a maximum quantum yield of 28% was observed for 19.2 nm Ca₂Nb₂O₇.