Morphology- and phase-controlled synthesis of monodisperse lanthanide-doped NaGdF4 nanocrystals with multicolor photoluminescence

Monodisperse, regular-shaped and well-crystallized nanocrystals (NCs) of lanthanide-doped NaGdF4 with diverse shapes and structures are synthesized in high boiling organic solvents 1-octadecene and oleic acid, through a competitive nucleation and growth pathway. The NCs can be manipulated to different morphologies and phase structures by using controlled variations in the reaction conditions such as composition of the solvent, temperature or reaction time. The NCs are thoroughly characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), selected area electron diffraction (SAED), high resolution TEM (HRTEM), field emission scanning electron microscopy (FESEM), IR spectroscopy, and photoluminescence. Possible mechanisms of NC nucleation and growth, size and shape evolution are proposed and tested. With different dopants, the NCs can show intensive multicolor down-conversion emissions under 254 nm UV excitation or up-conversion fluorescence under 980 nm NIR excitation, showing great promise in applications such as multi-analyte biolabels, staining, displays and other optical technologies.