Near-Infrared-to-Blue Upconversion in Colloidal BaYF5:Tm3+, Yb3+ Nanocrystals

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• 作者：Fiorenzo Vetrone ; Venkataramanan Mahalingam ; John A. Capobianco
• 刊名：Chemistry of Materials
• 出版年：2009
• 出版时间：May 12, 2009
• 年：2009
• 卷：21
• 期：9
• 页码：1847-1851
• 全文大小：189K
• 年卷期：v.21,no.9(May 12, 2009)
• ISSN：1520-5002

文摘

Tetragonal barium yttrium fluoride (BaYF₅) nanocrystals doped with 0.5 mol % Tm³⁺ and 15 mol % Yb³⁺ (BaYF₅:Tm³⁺, Yb³⁺) were synthesized using the thermal decomposition method yielding rectangular-shaped nanocrystals (15 nm × 5 nm) that can (up)convert near-infrared light to higher energies such as blue, via a process known as upconversion. The upconversion spectrum of the BaYF₅:Tm³⁺, Yb³⁺ nanocrystals, following excitation with 980 nm, revealed that the upconverted blue emission from the ¹G₄ → ³H₆ transition was more intense than the infrared ³H₄ → ³H₆ emission at high excitation densities (90 W/cm²) contrary to what is normally observed for Tm³⁺/Yb³⁺ codoped nanomaterials. On the other hand, the infrared emission dominates at lower excitation densities (15 W/cm²) demonstrating a lack of excited Yb³⁺ ions to carry on the upconversion beyond the ³H₄ excited state to the ¹G₄ excited state. A saturation of the upconversion process was observed in the power dependence studies at excitation densities above 57 W/cm², causing a deviation in the expected number of photons required for the upconversion process. The upconversion properties of BaYF₅:Tm³⁺, Yb³⁺ nanocrystals are elucidated and discussed.