Up-conversion quantum yields of SrF2:Yb3+,Er3+ sub-micron particles prepared by precipitation from aqueous solution†
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+:2H9/2, Er3+:2H11/2,4S3/2 and Er3+:4F9/2 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.