Down- and Up-Conversion Luminescent Nanorods

The rapidly increasing health care is now challenging the development of fluorescent biolabel materials used in diagnostics and bioanalysis such as immunoassay, fluorescence imaging and DNA or toxin detection. Due to their multicolor emission, high brightness and long lifetime, lanthanide ions based luminescent nanomaterials have tremendous promise as indicators and photon sources for numerous applications such as biolabels, light-emitting devices, sensor technology, and low-threshold lasers. However, when they are used in polymer-based luminescence devices, their strong luminescence is often quenched by the organic compounds. Therefore, doping the luminescent rare-earth ions into inorganic host materials can efficiently maintain their novel luminescence. But if their surface is not coated with organic compounds, these lanthanide-doped inorganic materials can not be dispersed in organic environment, which will further limits their application in polymer-based devices. So, it is very important to successfully prepare the rare-earth doped inorganic nanocrystals with good dispersibility in organic solvents. Up to now, lots of facile strategies have been developed for the preparation and application of the one-dimensional nanomaterials such as carbon nanotubes, semiconductor and metal nanocrystals, however, it is still a challenge for the synthesis of highly luminescent LaF3 and NaLaF4 nanorods with uniform shapes and sizes, high crystallinity, and especially controllable surface properties. Herein, we developed a facile one-pot strategy for the preparation of rareearth doped lanthanum fluoride (LaF3) and sodium lanthanum fluoride (NaLaF4) nanorods with controllable sizes and shapes. By doping different rare-earth ions, these nanorods can emit strong downconversion and upconversion fluorescence. For the coating surfactants on the surfaces, these asprepared nanocrystals are redispersible in nonpolar organic solvents such as cyclohexane to form a transparent colloidal solution, and can be easily aggregated by adding polar solvents such as ethanol, which facilitates their applications in polymer-based devices. Meanwhile, for their novel luminescence, they will also find great application in clinical and biological fields In brief, in water-ethanol-oleic acid mixing system, with a facile solvothermal technology, we successfully prepared the LaF3 and NaLaF4 nanorods by tuning sodium fluoride content and reaction time. By doping Ce-Tb and YbEr ion-pairs, novel downand up-conversion luminescence have been obtained, respectively. The crystal structure, shape and size of the resulting nanocrystals were quite sensitive to the reaction time, dopant concentration and NaF content. The results have been demonstrated by transmission electron microscopy (TEM) in Figure 1. In the case of low NaF content (2.0 mL, 1.0 mol L) and 6 h, only the short nanorods were obtained (Fig. 1a and b). High NaF content (2.7 mL, 1.0 mol L) and long reaction time (10 h) are beneficial for the formation of long nanorods (Fig. 1c and d). But with the elongation of the nanorods, their crystal phase has been already changed from LaF3 (Fig. 1a and b) to NaLaF4 C O M M U N IC A TI O N