Under 978 nm near-infrared (NIR) excitation, blue upconversion (UC) emissions from CaF2:Cu2+,Yb3+ were first observed at ∼420 nm.

White upconversion luminescence (UCL) was achieved under 980 nm excitation in the CaF2:Yb(3+)/Eu(3+) material using Y(3+) to adjust the luminescence performance. In this luminescent system, Yb(3+) not only plays the role of a sensitizer of Eu(3+), but also generates green fluorescence from Yb(3+) dimers (2-Yb(3+)) by cooperative transitions in the CaF2 matrix. One of the primary colors of green corresponds to the 2-Yb(3+) cooperative emission exactly. Eu(3+) 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 Y(3+) ions, and white UCL was realized when the concentration of Y(3+) was 1%.