Green and red up-conversion emissions of Er3+–Yb3+-codoped Al2O3 powders prepared by the nonaqueous sol–gel method

The 1 mol% Er3+- and 0–20 mol% Yb3+-codoped Al2O3 powders have been prepared by the nonaqueous sol–gel process using aluminum isopropoxide as precursor, acetylacetone as chelating agent, nitric acid as catalyzer, and hydrated erbium and ytterbium nitrate as dopant under isopropanol environment. The two crystalline types of doped Al2O3, γ and θ, and a stoichiometric compound, (Yb,Er)3Al5O12, were obtained for all the Er3+–Yb3+-codoped Al2O3 powders at the sintering temperature of 1000 °C. The maximal intensity of both the green and red up-conversion emissions centered at about 523, 545, and 660 nm was observed for the 1 mol% Er3+- and 10 mol% Yb3+-codoped Al2O3 powders. The intensity ratio of the red to green up-conversion emission (Ired/Igreen) increased with increasing the Yb3+ doping concentration for the Er3+–Yb3+-codoped Al2O3 powders. Furthermore, the intensity ratio of the green up-conversion emission at about 523 to 545 nm (I523/I545) was proportional to the Yb3+ doping concentration and pump electric current, which was associated with the elevated temperature of powders.