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Y2O3:Er3+ ultrafine phosphors with a varying Yb3+ ion concentration were prepared by a urea homogeneous precipitation method.The results of XRD show that all the samples are of a pure cubic structure and the average crystallite sizes can be calculated as 45,34,and 28 nm for Y2O3:Er3+ ultrafine phosphors with Yb3+ ion concentrations of 0,10%,and 20%,respectively.The lattice constant and cell volume of the ultrafine phosphors decrease with enhancing Yb3+ ion concentration.The upconversion luminescence spectra of all the samples were studied under 980 nm laser excitation.The strong green and red upconversion emission were observed,and attributed to the 2H11/2→4I15/2,4S3/2→4I15/2 and 4F9/2→4I15/2 transitions of Er3+,respectively.The intensity of red emission increases with increasing Yb3+ ion concentration.The effect of Yb3+ ion concentration on the structures and upconversion luminescence mechanism were discussed.