Hydrothermal Yb3+-Doped NaGd(WO4)2 Nano- and Micrometer-Sized Crystals with Preserved Photoluminescence Properties

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• 作者：Ftima Esteban-Betegn ; Carlos Zaldo ; Concepcin Cascales
• 刊名：Chemistry of Materials
• 出版年：2010
• 出版时间：April 13, 2010
• 年：2010
• 卷：22
• 期：7
• 页码：2315-2324
• 全文大小：1096K
• 年卷期：v.22,no.7(April 13, 2010)
• ISSN：1520-5002

文摘

Mild hydrothermal preparations using nitrate and chloride reagents as Gd³⁺ and Yb³⁺ sources lead to the synthesis of NaGd_1−xYb_x(WO₄)₂ (0.001≤ x ≤ 0.5) particles with tetragonal scheelite-like structure phase. Nearly neutral pH 7.5 conditions ensure the stability of this crystalline phase over a wide range of reaction times. Synthetical routes with both kind of reagents yield basically the same particle morphology sequences, although using Gd(Yb)-chlorides the presence of nanorods is more evident, whereas using Gd(Yb)-nitrates the faster growth rate favors well-defined micrometer-sized octahedral particles. The spectroscopic properties of Yb³⁺ in NaGd_1−xYb_x(WO₄)₂ synthesized micrometer-sized octahedra are equivalent to those obtained in bulk single crystals, showing a single exponential photoluminescence decay and ²F_5/2 lifetime τ ≈ 330 μs for 0.001 ≤ x ≤ 0.005 doped samples. The nanoparticles and nanorods formed with Gd(Yb)-nitrates and pH < 7 by short time annealing as well as in Gd(Yb)-chloride preparations show a strong reduction of the Yb³⁺ lifetime with regards to that observed in micrometer-sized octahedra or in single crystals, leading to nonexponential fluorescence decays when both nano- and micrometer-sized particles coexist. The use of raw Yb₂O₃ with increasing purity level in the hydrothermal process yields materials that show an increase in Yb³⁺ lifetime toward its radiative value.