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Issue 40, 2012
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Rapid microwave reflux process for the synthesis of pure hexagonal NaYF4:Yb3+,Ln3+,Bi3+ (Ln3+ = Er3+, Tm3+, Ho3+) and its enhanced UC luminescence

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Abstract

Pure hexagonal NaYF4:Yb3+,Ln3+ (Ln3+ = Er3+, Tm3+, Ho3+) crystals were obtained for the first time through a facile microwave (MW) reflux method at relatively low temperature (160 °C) and atmospheric pressure within only 50 min. By controllably increasing the NH4F content in the ethylene glycol (EG) solvent, the phase of as-prepared NaYF4:Yb3+,Ln3+ gradually transforms from cubic to hexagonal. Correspondingly, the up-conversion (UC) emission intensities of hexagonal NaYF4:Yb3+,Ln3+ (Ln3+ = Er3+, Tm3+, Ho3+) are increased by 10–12 times compared to those of the cubic phase. A possible growth mechanism for the phase transformation under these MW conditions has been proposed. Moreover, for the first time, we introduced Bi3+ ion into β-NaYF4:20%Yb3+,2%Ln3+ crystals. As expected, the UC emission of β-NaYF4:Yb3+,Ln3+,Bi3+ are about 10–40 times higher than those of Bi3+ free samples. It is found that tri-doping of Bi3+ doesn't change the basic emission of Ln3+ ions. XRD results gives evidence that tri-doping of Bi3+ ions can tailor the local crystal field and dissociate the Yb3+ and Ln3+ ion clusters, which is the main reason for the UC enhancement. This designed MW reflux method for the synthesis of β-NaYF4:20%Yb3+,2%Ln3+ can be applied to prepare other rare earth fluorides. The markedly enhanced UC luminescence through Bi3+ doping also provides an effective way to gain very bright UC emission.

Graphical abstract: Rapid microwave reflux process for the synthesis of pure hexagonal NaYF4:Yb3+,Ln3+,Bi3+ (Ln3+ = Er3+, Tm3+, Ho3+) and its enhanced UC luminescence

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Publication details

The article was received on 16 Jul 2012, accepted on 28 Aug 2012 and first published on 29 Aug 2012


Article type: Paper
DOI: 10.1039/C2JM34653B
J. Mater. Chem., 2012,22, 21613-21623

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    Rapid microwave reflux process for the synthesis of pure hexagonal NaYF4:Yb3+,Ln3+,Bi3+ (Ln3+ = Er3+, Tm3+, Ho3+) and its enhanced UC luminescence

    N. Niu, F. He, S. Gai, C. Li, X. Zhang, S. Huang and P. Yang, J. Mater. Chem., 2012, 22, 21613
    DOI: 10.1039/C2JM34653B

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