Oxyfluorotellurite glasses doped with different concentrations of Er3+ ions have been prepared and characterized. Strong infrared fluorescence at 1.55 mu m and efficient green and red upconversion fluorescence were observed under 975 mn excitation. The half maximum of the 1.53 mu m emission varies from 67 to 93 nm with change in Er3+ ions concentration. Decay curves of this emission remain single exponential but with reduced lifetimes with increase in Er 3+ ions concentration. Concentration quenching of lifetime of the 4I(13/2) level has been analyzed with the theory developed by Auzel et al. [F. Auzel, F. Bonfigli, S. Gagliari, G. Baldacchim, J. Lumin. 94-95 (2001) 293] and is found to be diffusion limited. A mechanism has been proposed to explain the upconversion process. (C) 2007 Elsevier B.V. All rights reserved.