Lanthanide-Doped Nanocrystals: Synthesis, Optical-Magnetic Properties, and Applications

Because of the potential applications of lanthanide-doped nanocrystals in display devices, optical communication, solid-state lasers, catalysis, and biological labeling, the controlled synthesis of these new nanomaterials has sparked considerable interest. Nanosized phosphorescent or optoelectronic devices usually exhibit novel properties, depending on their structures, shapes, and sizes, such as tunable wavelengths, rapid responses, and high efficiencies. Thus, the development of facile synthetic methods towards high-quality lanthanide-doped nanocrystals with uniform size and shape appears to be of key importance both for the exploration of their materials properties and for potential applications. This Account focuses on the recent development in our laboratory of the synthesis and applications of lanthanide-doped nanocrystals. Since 2005, when we proposed a general strategy for nanocrystal synthesis via a liquid solid solution process, a range of monodisperse and colloidal lanthanide-doped fluoride, oxide, hydroxide, orthovanadate, thiooxide, borate, and phosphate nanocrystals have been successfully prepared. By rationally tuning the reaction conditions, we have readily synthesized nanostructures, such as hollow microspheres, nanorods, nanowires, hexagonal nanoplates, and nanobelts. By adjusting the different colloidal nanocrystal mixtures, we fabricated unique binary nanostructures with novel dual-mode luminescence properties through a fadle ultrasonic method. By tridoping with lanthanide ions that had different electronic structures, we successfully achieved beta-NaYF4 nanorods that were paramagnetic with tuned upconversion luminescence. We have also used NaYF4:Yb3+/Er3+ conbined with magnetite nanoparticles as a sensitive detection system for DNA: NaYF4:Yb3+/Er3+ and Fe3O4 nanoparticles were modified with two different DNA sequences. Then, the modified NaYF4:Yb3+/Er3+ nanoparticles were conjugated to the modified Fe3O4 nanoparticles. These binary nanoparticles can be hybridized with a third DNA (target DNA) molecule and separated with the assistance of a magnetic field. In addition, a novel fluorescence resonance energy transfer (FRET) method for nonenzymatic glucose determination has been developed by using the glucose-modified LaF3:Ce3+/Tb3+ nanocrystals. By using bioconjugated NaYF4:Yb3+/Er3+ nanoparticles as the energy donor and bioconjugated gold nanoparticles as the energy acceptor, we successfully developed a simple and sensitive fluorescence resonance energy transfer (FRET) biosensor for avidin. Meanwhile, we also carried out preliminary studies to investigate possible applications of lanthanide-doped nanocrystals in catalysis and in dye-sensitized solar cells.