Investigation of sensitizer ions tunable-distribution in fluoride nanoparticles for efficient accretive three-center energy transfer

Cooperative upconversion luminescence of Yb3+-Yb3+ couples and three-center energy transfer mechanisms have been deeply investigated in Yb3+ doped and Yb3+-Tb3+ co-doped β-PbF2 nanoparticles. As sensitizer ions, the distribution of Yb3+ ions, which is a key factor that affects the cooperative upconversion luminescence and three-center energy transfer processes, can be tuned by the structure of nanoparticles. Based on the three-center distributions in tetragonal PbYbxTb1−xF5 nanoparticles, two different energy transfer models, Cooperative Energy Transfer (CET) and Accretive Energy Transfer (AET) mechanisms were established. Especially, AET model is observed and verified in this work for the first time. Experimental results obtained from photoluminescence spectroscopy study are in agreement with the theoretical calculations by applying rate equations in these models, strongly supporting the proposed three-center energy transfer mechanisms. The sensitization between Yb3+ ions only existing in AET process can greatly improve the energy transfer rates, further to enhance the quantum efficiency. The results that the calculated luminescence quantum efficiency in AET quantum cutting process is much higher than that in CET process (134% and 104%, respectively), can benefit for further increasing the conversion efficiency of c-Si solar cells.