Controlled synthesis of hexagon shaped lanthanide-doped LaF3 nanoplates with multicolor upconversion fluorescence

Yb - Er, Yb - Ho and Yb - Tm co- doped LaF3 IR- to- visible upconversion fluorescent nanocrystals with well- crystallized hexagonal phases were synthesized by a solvothermal technique, which was based on the decomposition of rare- earth trifluoroacetates. During this reaction the generation of fluoride ions and the nucleation of the LaF3 occurred almost simultaneously. Through a phase transition procedure, nanoplates with well- crystallized hexagon shape and an average edge length of 20 - 30 nm were obtained because the nucleation and growth processes were slow. The size, morphology and phase transition of the rare- earth fluorides were discussed in relation to solvents, reaction time and temperature and a reaction mechanism was proposed. Furthermore, these nanoplates could be easily dispersed in organic solutions and formed a transparent colloidal solution. Under 980 nm IR excitation, multicolor emission bands can be observed for different codopants, which show potential applications as color displays, light- emitting diodes, optical storage, optoelectronics and biolabels.