Upconversion luminescence in CaSc2O4 doped with Er3+ and Yb3+

Upconversion luminescence in ceramic samples of CaSc2O4:Er:Yb is investigated. The main upconversion mechanisms, as well as the influence of various cross-relaxation processes on the luminescence emission are discussed. The optimum Yb3+ concentration was found at 5%. The red/green intensity ratio is found to be mainly influenced by the energy back-transfer process ((2H11/2, 4S3/2) (Er3+), 2F7/2 (Yb3+))→(4I13/2 (Er3+), 2F5/2 (Yb3+)). A simple mathematical model based on rate equations is developed and used for the discussion of the experimental results. The maximum upconversion efficiency is 0.94% for the CaSc2O4:Er(1%):Yb(5%) sample.