White upconversion luminescence in CaF₂:Yb³⁺/Eu³⁺ powders: Via the incorporation of Y³⁺ ions

White upconversion luminescence (UCL) was achieved under 980 nm excitation in the CaF₂:Yb³⁺/Eu³⁺ material using Y³⁺ to adjust the luminescence performance. In this luminescent system, Yb³⁺ not only plays the role of a sensitizer of Eu³⁺, but also generates green fluorescence from Yb³⁺ dimers (2-Yb³⁺) by cooperative transitions in the CaF₂ matrix. One of the primary colors of green corresponds to the 2-Yb³⁺ cooperative emission exactly. Eu³⁺ acts as an activator for emitting red and blue fluorescence simultaneously. Interestingly, the color of the UCL can be controlled by adjusting the doping concentration of Y³⁺ ions, and white UCL was realized when the concentration of Y³⁺ was 1%.