• Original Paper: Sol-gel and hybrid materials for optical, photonic and optoelectronic applications
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Reverse microemulsion synthesis of mixed α and β phase NaYF4:Yb,Er nanoparticles: calcination induced phase formation, morphology, and upconversion emission


A novel “water-in-oil” type reverse microemulsion assisted synthesis detail on the formation of mixed cubic and hexagonal (α + β) phase NaYF4:Yb,Er nanoparticles and their upconversion emission properties are presented. The effect of surfactants, fluorine precursors on the crystallographic phase fraction, crystallite size of NaYF4:Yb,Er nanoparticles on red upconversion emission is discussed. The NaYF4:Yb,Er nanoparticles synthesized with CTAB, and oleic acid surfactants give larger crystallite size and moderate hexagonal/cubic phase fraction. It has resulted very intense upconversion red emission. The oleic-acid-free preparation of NaYF4:Yb,Er nanoparticles resulted highly-agglomerated nanoparticles and low crystallite size, which gives less-intense upconversion emission. The cubic and hexagonal phase fractions of NaYF4:Yb,Er depends on surfactants, microemulsion, molar concentrations of precursors, and post-calcination. All these factors influence the mondispersibility and upconversion red emission properties. The 980 nm laser pump power dependent upconversion emission studies have confirmed the typical two-photon behavior in α + β phase NaYF4:Yb,Er nanoparticles. Their decay life was also measured to correlate the upconversion red emission intensity. The effect of mixed α + β phase NaYF4:Yb,Er nanoparticles on the 1530 nm NIR emission is also presented.


  • Mixed phase NaYF4:Yb,Er nanoparticles were prepared by reverse microemulsion.

  • The hexagonal/cubic phase fraction is changed by varying surfactants/precursors.

  • Visible upconversion and NIR emissions are observed under 980 nm excitation.

  • CTAB-OA assisted synthesis yielded uniform nanospheres and strong upconversion.

  • OA free preparation resulted in agglomerated particles affects the upconversion.

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The author MG extends his sincere gratitude for the award of research fellowship and JS is grateful to UGC-UPE Phase II program. Authors are grateful to Professor C. Santhosh, Head of the Department of atomic and molecular spectroscopy, Manipal Academy of Higher Education, India for UV-Vis-NIR absorption characterization. GAK and DKS acknowledge the (NSF-PREM) grant NO-DMR-0934218.

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Correspondence to J. Senthilselvan.

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Gunaseelan, M., Yamini, S., Kumar, G.A. et al. Reverse microemulsion synthesis of mixed α and β phase NaYF4:Yb,Er nanoparticles: calcination induced phase formation, morphology, and upconversion emission. J Sol-Gel Sci Technol (2020). https://doi.org/10.1007/s10971-020-05340-w

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  • NaYF4:Yb,Er
  • Mixed phase
  • Upconversion
  • Oleic acid
  • CTAB
  • Microemulsion