Manipulating energy transfer in lanthanide-doped single nanoparticles for highly enhanced upconverting luminescence.

Energy transfer (ET) is of fundamental importance in tuning the optical performance of lanthanide-doped upconversion nanoparticles (UCNPs). However, the fine control and manipulation of the ETs particularly for deleterious cross-relaxation type ETs (CR-ETs) in lanthanide-doped UCNPs remains a formidable challenge to date. Herein, we demonstrate a rational design strategy to manipulate the deleterious CR-ETs in lanthanide-doped UCNPs, by fine-tuning the distances at an extremely large length scale (>20 nm) among multiple lanthanide dopants that are simultaneously embedded into one single nanoparticle with specially designed multilayer nanostructures. The successful inhibition of the CR-ETs leads to a significantly enhanced upconversion luminescence signal with an intensity ∼70 times higher than that of co-doped conventional UCNPs. This finding paves a new way for the better control of the ETs in lanthanide-doped nanoparticles, and offers the possibility of constructing a series of promising single-nanocrystal-based anti-counterfeiting barcodes with well-identified UC emission color and lifetime outputs.