Recently, considerable attention has been paid to the synthesis and research of various rare-earth （RE） doped fluoride nanomaterials because of their high refractive index and appropriate phonon energy, which have potential applications in optics, optoelectronics, microelectronics, and tribology. Many methods have been utilized to synthesize the nanomaterials of RE doped fluorides with controllable sizes, shapes, and nanostructures. Comparatively, the microwave irradiation （MWI） method is simple, fast, and unique in its potential for large-scale synthesis without suffering thermal gradient effects.
This paper reports that hexagonal-phase LaF3：Yb0.20^3＋,Er0.02^3＋ and LaF3：Yb0.20^3＋, Tm0.02^3＋ nanocrystals （NCs） were synthesized via a hydrothermal method. The transmission electron microscopy, selected area electron diffraction, powder x-ray diffraction, and thermogravimetric analysis are used to characterize the NCs. Under 980 nm excitation, the Yb^3＋/Er^3＋ and Yb^3＋/Tm^3＋ codoped NCs colloidal solutions present bright green and blue upconversion fluorescence, respectively. These NCs show efficient infrared-to-violet and infrared-to-visible upconversion. The upconversion fluo- rescence mechanisms of LaF2：Yb0.20^3＋, Er0.02^3＋ and LaF3：Yb0.20^3＋,Tm0.02^3＋ NCs are investigated with a 980-nm diode laser as excitation source.
