Improving monochromaticity of upconversion luminescence by codoping Eu3+ ions in Y2O3:Ho3+, Yb3+ nanocrystals

Upconversion (UC) luminescence of Y2O3:Ho3+, Yb3+ nanocrystals codoped with different concentrations of Eu3+ ions were investigated to improve the monochromaticity of the UC emission. The results show that the monochromaticity, quantified by a parameter SR, increases as the concentration of Eu3+ ions becomes higher, which is due to the energy transfer between 5I7 (Ho3+) and 7F6 (Eu3+). The energy transfer accelerates the relaxation of Ho3+ ions from the 5I7 to 5I8 state and then quenches the red emission. The influence of the Eu3+ concentration on the pump power dependence of the red UC fluorescence in Y2O3:Ho3+, Yb3+, Eu3+ nanocrystals is verified using the steady-state rate equation theory.