Abstract
An interface-controlled reaction in normal microemulsions (water/ethanol/sodium oleate/oleic acid/n-hexane) was designed to prepare NaYF4:Yb3+, Er3+ upconversion nanoparticles. The phase diagram of the system was first studied to obtain the appropriate oil-in-water microemulsions. Transmission electron microscopy and X-ray powder diffractometer measurements revealed that the as-prepared nanoparticles were spherical, monodisperse with a uniform size of 20 nm, and of cubic phase with good crystallinity. Furthermore, these nanoparticles have good dispersibility in nonpolar organic solvents and exhibit visible upconversion luminescence of orange color under continuous excitation at 980 nm. Then, a thermal treatment for the products was found to enhance the luminescence intensity. In addition, because of its inherent merit in high yielding and being economical, this synthetic method could be utilized for preparation of the UCNPs on a large scale.
Highlights
The synthesis and spectroscopy of NaYF4:Yb3+, Er3+ upconversion nanoparticles (UCNPs) have attracted a tremendous amount of attention because of their potential use in bioanalysis and medical imaging recently [1,2,3,4,5]
Because of the complexity of the fivecomponent system, the phase diagram was simplified to a ternary phase diagram, which is composed of total oleic acid (OA), water plus ethanol, and n-hexane
The NaOA/OA molar ratio is always 2:3, and the total volume of OA is considered as the surfactant volume
Summary
The synthesis and spectroscopy of NaYF4:Yb3+, Er3+ upconversion nanoparticles (UCNPs) have attracted a tremendous amount of attention because of their potential use in bioanalysis and medical imaging recently [1,2,3,4,5]. Upconversion was first recognized and formulated by Auzel in the mid-1960s [6], which is a process where low energy light, usually near-infrared (NIR) or infrared (IR), is converted to higher energies, ultraviolet (UV) or visible, via multiple absorptions or energy transfers. The synthesis of various inorganic nanoparticles in normal microemulsions attracts our attention [21]. Owing to the polarity inverse caused by the neutralization, the particles can be
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