Lutetium doping for making big core and core–shell upconversion nanoparticles

A novel strategy for making big core and core–shell upconversion nanoparticles (UCNs) by lutetium doping has been developed. The size of the core UCNs is easily tuned in the increasing direction with enhanced luminescence by rational lutetium doping. Use of NaLuF₄ as a shell material provides a promising solution to the difficulty of coating a shell onto big core UCNs with tremendous thickness. This can lead to the fabrication of UCNs with well-designed core–shell structures, with multiple layers and desired thickness, for various applications such as optical encoding, multiplexed biodetection, microarrays, and flow cytometry.