Controlled size and morphology, and phase transition of YF3:Yb3+,Er3+ and YOF:Yb3+,Er3+ nanocrystals for fine color tuning
Lanthanide rare-earth (RE) based upconversion nanocrystals (UCNCs) have the ability to generate visible emission as well as a wide range of applications under near-infrared excitation. However, each lanthanide ion has a unique set of energy levels and generally exhibits a set of sharp emission peaks. Nowadays, it is very important to finely tune the upconversion (UC) properties through controlling the particle size, crystalline phase and shape of UCNCs. Herein, we reported the systematic synthesis and fine control of monodisperse rare-earth doped fluoride and oxyfluoride nanocrystals (NCs) in the same reaction system. When the ratios of oleic acid (OA) to oleylamine (OM) decreased from 4 : 1 to 3 : 8, the shapes of NCs changed from rhombic nanoplates to small spherical nanoparticles (~2 nm), while the crystalline phases changed from the orthorhombic phase (YF3) to the tetragonal phase (YOF). Furthermore, it is interesting to observe that the emission color changed from green to red with the transformation of both the crystalline phase and shape, which can broaden the applications of rare-earth based nanomaterials ranging from displays to bioimaging.