Up-conversion quantum yields of SrF2:Yb3+,Er3+ sub-micron particles prepared by precipitation from aqueous solution

Abstract

Herein, we report near-infrared-to-visible up-conversion (UC) in SrF₂:Yb³⁺,Er³⁺ sub-micron crystals prepared via a facile route in an aqueous solution. Subsequent calcination at 600 °C allows us to achieve good UC quantum yields, reaching 2.8% at an excitation power density of 10 W cm⁻² for a sample doped with 2 mol% of Yb³⁺ and 2 mol% of Er³⁺. This UC quantum yield of SrF₂:Yb³⁺,Er³⁺ is in the range of record UC quantum yields reported in the literature for standard host systems such as La₂O₂S, BaY₂ZnO₅ and NaYF₄ phosphors. Interestingly, the 2 mol% of Yb³⁺ required to achieve optimal UC in the SrF₂ host is much lower than the amount of Yb³⁺ required in the other host systems. Furthermore, we studied the population and depopulation kinetics of the Er³⁺:²H_9/2, Er³⁺:²H_11/2,⁴S_3/2 and Er³⁺:⁴F_9/2 states using time-resolved photoluminescence measurements in order to provide insight into the UC mechanism. The facile preparation method combined with high UC quantum yield makes SrF₂:Yb³⁺,Er³⁺ materials attractive candidates for solar energy harvesting, sensors, solid state lasers, and luminescent markers.