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

Abstract

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.