Abstract
Hexagonal NaYF4:Nd3+/Yb3+/Er3+ microcrystals and nanocrystals with well-defined morphologies and sizes have been synthesized via a hydrothermal route. The rational control of initial reaction conditions can not only result in upconversion (UC) micro and nanocrystals with varying morphologies, but also can produce enhanced and tailored upconversion emissions from the Yb3+/Er3+ ion pairs sensitized by the Nd3+ ions. The increase of reaction time converts the phase of NaYF4:Nd3+/Yb3+/Er3+ particles from the cubic to the hexagonal structure. The added amount of oleic acid plays a critical role in the shape evolution of the final products due to their preferential attachment to some crystal planes. The adjustment of the molar ratio of F−/Ln3+ can range the morphologies of the β-NaYF4:Nd3+/Yb3+/Er3+ microcrystals from spheres to nanorods. When excited by 808 nm infrared laser, β-NaYF4:Nd3+/Yb3+/Er3+ microplates exhibit a much stronger UC emission intensity than particles with other morphologies. This phase- and morphology-dependent UC emission holds promise for applications in photonic devices and biological studies.
Highlights
Lanthanide doped upconversion (UC) materials have attracted increasing interest due to their ability to convert low-energy excitations into high-energy emissions at shorter wavelength [1,2,3]
Very few studies reported on sizeand morphology-controlled synthesis of UC Nd3+-sensitized particles with tailored luminescence when excited at ~808 nm
We show that variations of the oleic acid ligand and the concentration ratio of F−/Ln3+ play a synergistic role in defining the morphologies of resulting particles
Summary
Lanthanide doped upconversion (UC) materials have attracted increasing interest due to their ability to convert low-energy excitations into high-energy emissions at shorter wavelength [1,2,3]. This unique property makes UC materials suitable for a wide range of applications, such as biological sensing [4,5], in vivo imaging [6,7], drug delivery [8,9], and photodynamic therapy [10,11]. Very few studies reported on sizeand morphology-controlled synthesis of UC Nd3+-sensitized particles with tailored luminescence when excited at ~808 nm.
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