Controlled Synthesis, Formation Mechanism, and Great Enhancement of Red Upconversion Luminescence of NaYF4:Yb3+, Er3+ Nanocrystals/Submicroplates at Low Doping Level

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• 作者：Junwei Zhao ; Yajuan Sun ; Xianggui Kong ; Lijin Tian ; Yu Wang ; Langping Tu ; Jialong Zhao ; Hong Zhang
• 刊名：Journal of Physical Chemistry B
• 出版年：2008
• 出版时间：December 11, 2008
• 年：2008
• 卷：112
• 期：49
• 页码：15666-15672
• 全文大小：253K
• 年卷期：v.112,no.49(December 11, 2008)
• ISSN：1520-5207

文摘

Strong red upconversion luminescence of rare-earth ions doped in nanocrystals is desirable for the biological/biomedical applications. In this paper, we describe the great enhancement of red upconversion emission (⁴F_9/2 → ⁴I_15/2 transition of Er³⁺ ion) in NaYF₄:Yb³⁺, Er³⁺ nanocrystals at low doping level, which is ascribed to the effectiveness of the multiphonon relaxation process due to the existence of citrate as a chelator and cross relaxation between Er³⁺ ions. The dissolution−recrystallization transformation, governing both the intrinsic crystalline phase (cubic and/or hexagonal phase) and the growth regime (thermodynamic vs kinetic), is responsible for the phase control of the NaYF₄ crystals. The possible formation mechanism of the NaYF₄ crystals and the role of trisodium citrate which acts as a chelating agent and shape modifier are discussed in detail. It is also found that the α → β phase transition is favored by the high molar ratio of fluoride to lanthanide and high hydrothermal temperature as well as long hydrothermal time.