A general strategy for tailoring upconversion luminescence in lanthanide-doped inorganic nanocrystals through local structure engineering

A local structure around lanthanide (Ln(3+)) emitters in Ln(3+)-doped upconversion nanocrystals (UCNCs) is of fundamental importance in tailoring their upconversion luminescence (UCL) features. However, a general strategy responsible for the local-structure-dependent UCL in Ln(3+)-doped UCNCs has not been conclusively established to date. Herein, we report a new class of alkaline zirconium fluoride-based Yb-3(+)/Er3+ co-doped UCNCs featuring a diversity of crystallographic structures for Ln(3+) ion doping, which thereby allow us to thoroughly understand the origin underlying the local-structure-dependent UCL of the Er3+ ion for the first time. We reveal that the high-symmetry crystal lattice of Yb-3(+)/Er3+ co-doped UCNCs may incur the large UCL red-to-green intensity ratio of Er3+ regardless of their identical elemental compositions. In combination with the first-principles calculations, we show that such local-structuredependent UCL of Er3+ is primarily due to the varied electronic band structures induced by the Yb-3(+)/Er3+ doping in different crystallographic structures of alkaline zirconium fluorides. These findings may open up a new avenue for constructing high-quality UCNCs with a tailored UCL profile and lifetime for diverse applications.