Facile synthesis and properties of spherical assemblies of NaYF4nanocrystals with consistent crystalline orientation

Abstract

Synthesis of NaYF₄ nanocrystals with well-defined shapes and/or architectures has been of great interest in recent years, owing to their unique optical properties and wide applications in biological fields. NaYF₄ nanocrystals with conventional morphologies have been developed through a variety of chemical or physical methods; however, it still remains challenging to build complex architectures by assembly well-defined NaYF₄ nanocrystals in a simple system. Here, we present a facile solution-based method for synthesizing assembled NaYF₄ nanocrystals at large scale. These assemblies exhibit a spherical appearance within which NaYF₄ nanocrystals are tightly attached and arranged along the same crystalline orientation. This interesting hierarchical structure not only offers a high surface area and easy modification surface, but also provides a new efficient host for doping various lanthanide ions to give strong down- or up-conversion emissions. It is anticipated that these unique assembled NaYF₄ nanostructures will serve as biolabels in various biomedical applications.