Luminescence properties of Ca0.65La0.35F2.35:Yb, Er with enhanced red emission via upconversion

Yb³⁺/Er³⁺ codoped Ca_0.65La_0.35F_2.35 materials with intense red emission via upconversion were prepared by a high temperature solid-state method. Based on the upconversion luminescence properties investigations, it was found that, under 980 nm excitation, Ca_0.65La_0.35F_2.35:20 mol.%Yb³⁺, xEr³⁺ showed intense red upconversion luminescence, which was ascribed to ⁴F_9/2 → ⁴I_15/2 transition of Er³⁺, although both green and red emissions could be detected. It was also found that the green and red emissions originated the two photon processes, and the ground-state absorption (GSA), excited-state absorption (ESA) and energy transfer (ET) processes between Er³⁺/Yb³⁺ ions and Er³⁺/Er³ ions were involved in the enhanced red emission mechanism.