Abstract: The Y³⁺ co-doping to the 0.1 and 1.0mol% Er³⁺-doped Al₂O₃ powders with
the molar ratio of (0～10): 1 for Y³⁺ and Er³⁺ was performed in the non-aqueous sol-gel progress using the aluminium isopropoxide Al(OC₃H₇)₃-derived Al₂O₃ sols with the addition of hydrated erbium nitrate Er(NO₃)₃·5H₂O together with yttrium nitrate Y(NO₃)₃·5H₂O. The effects of Y³⁺ co-doping on the phase structure and photoluminescence (PL) of the Er³⁺-doped Al₂O₃ powders were investigated by X-ray diffraction (XRD) and PL measurement. The Y³⁺ addition in the Er³⁺-doped Al₂O₃ powders suppressed the crystallization of γ-(Er,Al)₂O₃ and θ-(Er,Al)₂O₃ phases. The enhancement of the PL properties by Y³⁺ co-doping is related to Er³⁺concentration in the Er³⁺-doped Al₂O₃ powders. For the 1mol% Er³⁺-doped Al₂O₃ powders, co-doping Y³⁺ with the concentration up to 10mol% is incorporated in the mixture　of γ and θ phases, resulting in an increase of both the intensity and full width at half maximum (FWHM) of PL spectra. The PL intensity for the 1mol% Er³⁺-doped Al₂O₃ powders by 10mol% Y³⁺ co-doping is enhanced by 50 times and almost 10 times higher than that of the 0.1mol%Er3+-doped Al₂O₃ powders, and the FWHM is enhanced by a gain of 15nm in comparison with those for the 1mol% Er³⁺-doped powders. However, for the 0.1mol% Er³⁺-doped Al₂O₃ powders, no significant change in the intensity and FWHM of PL spectra is observed with all the Y³⁺ incorporations. The improvement of intensity and FWHM of PL spectra for the Er³⁺-doped Al₂O₃ powders by Y³⁺ co-doping　is attributed to the improved dispersion and disordered local structure around Er³⁺ in the matrix of the Er³⁺-doped Al₂O₃ powders, respectively.