Single-band red upconversion luminescence of Yb3+–Er3+via nonequivalent substitution in perovskite KMgF3 nanocrystals

Abstract

Single-band red upconversion (UC) emission of Er³⁺ has been successfully achieved in Yb³⁺/Er³⁺ codoped KMgF₃ nanocrystals via a nonequivalent substitution strategy, in which lanthanide ions probably aggregate, as evidenced by density functional theory calculations and upconversion dynamic processes. The aggregation of Yb³⁺/Er³⁺ would cause large cross-relaxation probabilities among the lanthanide ions when photo-excited, resulting in the disappearance of the green emission and the population of the red emitting level of Er³⁺. Interestingly, the single-band feature is independent of the dopant concentration and pump power. The possible UC mechanism is discussed in detail according to nanocrystal morphology, ion radii, lattice parameters and decay lifetime studies of the Yb³⁺–Er³⁺ doped analogous compounds (KMgF₃, KZnF₃ and KCdF₃). It could be concluded that Yb³⁺/Er³⁺ ions tend to aggregate in KMgF₃, resulting in the largest ratio of red to green UC emission. This research may give a perspective toward tuning the UC emission of lanthanide ions.