Enhanced Up-Conversion Emission of Er³⁺-Doped Al₂O₃ Powders by Y³⁺ Codoping Prepared in a Non-Aqueous Sol-Gel Process

1 mol% Er3+- and 0–10 mol% Y3+-codoped Al2O3 powders is prepared in a non-aqueous sol–gel method. Two crystalline types of doped Al2O3,  and θ, are obtained for the 0–10 mol% Y3+-codoped Al2O3 powders sintered at the sintering temperature of 1000 °C by x-ray diffraction analysis. The green and red up-conversion emissions centered at about 550 and 670 nm increase with Y3+ codoping concentration, and the maximal intensity of both the green and red up-conversion emissions is obtained as about 100 and 10 times higher than that of the 1 mol% Er3+-doped Al2O3 powders, respectively. The enhancement in the green and red up-conversion emissions is ascribed to the improved dispersion of Er3+ in Er3+–Y3+-codoped Al2O3 powders.