Synthesis of dye-loaded NaYF4:Yb, Er superparticles for tunable upconversion emissions

Spherical superparticles consisting of small NaYF₄:Yb, Er nanocrystals are developed with an emulsion method. Within each superparticle, many individual upconversion nanocrystals are condensed together and lots of small vacancies are simultaneously produced because of the packing of primary nanocrystals. Through the loading fluorescent dyes inside the vacancies of these superparticles during assembly, one can fine-tune the upconversion fluorescence of these superparticles. Nearly single-band red upconversion emission can also be achieved by loading suitable amounts of dyes in these superparticles.