Controlling the morphology of core-shell nanoparticles

Abstract

In recent years, there have been many research experiments and studies conducted on lanthanide doped upconversion materials due to its upconversion (UC) property. UC is an optical process which can convert the absorbed light with long wavelength into a light with short wavelength and UC has great potential in wide applications, such as bio-sensing and bio-imaging. Usually, to improve the UC efficiency of the synthesized UC nanoparticles, we need to design a core-shell structure to prevent UC nanoparticles from the surface quenching effect. Different core-shell structure designs can have different improvements on the UC nanoparticles due to different morphologies they may result in. In this project, we studied the lattice mismatch as the key factor in controlling the morphology of the core-shell nanoparticles. We have synthesized four types of core-shell nanoparticles with the same UC cores, NaYF4:Yb/Er(28:2), and the shells with different components, NaYF4:Yb/Er(28:2), NaYF4, NaLuF4 and NaGdF4. Both Transmission Electron Microscopy (TEM) and X-Ray Diffractometer (XRD) examination were carried out to inspect the morphologies of different types of core-shell nanoparticles and to determine the crystalline information of the shell components. Besides we also conducted Photoluminescence (PL) test to exam the influence of the different morphologies on the UC efficiency. The results from the experiment suggest that the lattice mismatch between core and shell components plays a very important role in controlling the final morphology of the core-shell nanoparticles. Different degrees of lattice mismatch due to different sizes of the atoms in the crystal structure with same phase can lead to different crystal growth preferences. Our results provide very useful suggestion in designing the core-shell structure for modifying the optical properties UC lanthanide doped nanoparticles by controlling their morphologies through controlling the lattice mismatch between core and shell materials.