Phase transition of Er3+-doped Al2O3 powders prepared by the non-aqueous sol–gel method

The Er3+-doped Al2O3 powders have been prepared by the non-aqueous sol–gel method using the aluminum isopropoxide as precursor, acetylacetone as chelating agent, nitric acid as catalyzer, and hydrated erbium nitrate, as dopant under isopropanol environment. The phase structure and phase transition of the Er3+-doped Al2O3 powders were investigated by using thermogravimetry/differential thermal analysis (TG/DTA), Fourier transform infrared spectroscopy (FT-IR), and X-ray diffraction (XRD). The phase contents diagram for the Er-doped Al–O system with the doping concentration up to 5 mol% was described at the sintering temperature from 550 to 1250 °C. There were the three crystalline types of Er3+-doped Al2O3 phases, γ-, θ- and α-(Al, Er)2O3, and the two relative stoichiometric compounds composed of Al, Er, and O, ErAlO3 and Al10Er6O24 phases in the Er–Al–O phase contents diagram. The Er3+ doping suppressed crystallization of the γ and θ phases and delayed phase transition of the γ → θ and θ → α. The increased Er3+ doping concentration and the elevated sintering temperature enhanced the precipitation of the ErAlO3 and Al10Er6O24 phases. The preparation procedure for the Er3+-doped Al2O3 powders in the non-aqueous sol–gel process, including chelating, hydrolysis, peptization, doping and gelation, has a significant effect on the phase formation and its transition for the Er3+-doped Al2O3 powders.