Modification of NaYF4:Yb,Er@SiO2 Nanoparticles with Gold Nanocrystals for Tunable Green-to-Red Upconversion Emissions

Lanthanide-doped upconversion nanocrystals which can convert near-infrared lights to visible lights have attracted growing interest because of their great potentials in biomedical engineering. However, it remains a grand challenge to maneuver the intensity ratio between different emission lines and enable tunable upconversion functions. Herein, we present a facile method to integrate NaYF4:Yb, Er upconversion nanocrystals with gold nanocrystals for constructing NaYF4:Yb,Er@SiO2@Au hybrid nanostructures, in which a silica layer on NaYF4:Yb,Er nanocrystals serves as an interface for gold decoration. The green-to-red emissions of the upconversion nanocrystals can be conveniently tuned by altering the amount of surrounding gold nanocrystals. We further demonstrate the capability of utilizing both green and red emission lines for spontaneous signaling in an emitter-quencher-based bioassay by implementing this novel hybrid nanostructure. It is anticipated that the controllability in upconversion fluorescence in this hybrid nanostructure may provide a platform for widely exploring applications in biological imaging, detection, and sensing.