Infrared-to-visible and infrared-to-violet upconversion fluorescence of rare earth doped LaF₃ nanocrystals

This paper reports that hexagonal-phase LaF_3:Yb^3 + _0.20, Er^3 + _0.02 and LaF_3:Yb^3 + _0.20, Tm^3 + _0.02 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 fluorescence mechanisms of LaF_3:Yb^3 + _0.20, Er^3 + _0.02 and LaF_3:Yb^3 + _0.20, Tm^3 + _0.02 NCs are investigated with a 980-nm diode laser as excitation source.