Tandem energy upconversion in a conjugated polymer-sensitized core/shell nanocrystal

We developed a novel hybrid system combining inorganic NaYF₄: Yb³⁺, Er³⁺@NaYF₄:Yb³⁺ core/shell nanocrystal with organic diketopyrrolopyrrole-based conjugated polymer (PDFT). Directional energy transfer from light-harvesting PDFT to Yb³⁺ ions in the shell, and finally to the emitter Er³⁺ ions in the core takes place in this hybrid system so as to boost UCNPs upconversion efficiency. The number of antennas (concentration of PDFT) was optimized to maximize tandem energy transfer efficiency. PDFT increase the emission intensity of UCNPs by ~39-fold and having a wide range of excitable spectrum range (600–850 nm). Importantly, polymer sensitized upconversion nanosystems was much more stable compared to traditional small molecule sensitized ones, which can be important for their further applications.