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Boosting Luminance Energy Transfer Efficiency in Upconversion Nanoparticles with an Energy Concentrated Zone.

Despite the successful application of upconversion nanoparticles (UCNPs), their low energy transfer efficiency is still a bottleneck. Here we design a multilayer structure of UCNPs, including an inert NaYF4:Gd core and an "Energy concentrated zone" (ECZ), for efficient energy concentration. The ECZ is composed of an emitting layer NaYF4:Yb,Er and an absorption layer NaYF4:Nd,Yb with antenna 800CW to manipulate the energy transfer. The stable and tight packing of 800CW linked originally with a bisphosphonate ligand improves greatly the transfer efficiency. The proximity of the emitting layer to both surface antenna and accepter also decreases energy depletion. Compared to classical UCNPs, the ECZ UCNPs show 3600 times higher luminescence intensity with an energy transfer efficiency near 60%. As proof-of-concept, this structure has led to an exciting sensitivity for analytical application and an outstanding capability to overcome the limitation of photodynamic therapy in hypoxia.