Self-assembly of LaF3:Yb,Er/Tm nanoplates into colloidal spheres and tailoring their upconversion emissions with fluorescent dyes

Colloidal nanoparticle clusters (CNCs) of LaF3 nanoplates are developed by an emulsion method. Owing to their highly anisotropic shape, these nanoplates can be assembled into spherical particles with various assembly patterns. Investigation on the formation mechanism suggests that two kinds of surfactant, one from the surface of nanocrystals and one from the emulsion, play important roles in directing the assembly patterns of these nanoplates. After doping with lanthanide ions, LaF3:Yb,Er/Tm CNCs after assembly can show enhanced upconversion fluorescence compared to their counterparts in a free-standing form. Through loading fluorescent dyes in mesoporous pores of these LaF3 CNCs, one can finely tune their upconversion emissions through the FRET process.