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

Abstract

A local structure around lanthanide (Ln³⁺) emitters in Ln³⁺-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 Ln³⁺-doped UCNCs has not been conclusively established to date. Herein, we report a new class of alkaline zirconium fluoride-based Yb³⁺/Er³⁺ co-doped UCNCs featuring a diversity of crystallographic structures for Ln³⁺ 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 Yb³⁺/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-structure-dependent UCL of Er³⁺ is primarily due to the varied electronic band structures induced by the Yb³⁺/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.