A new 1.75 mum infrared emission transition of Y2O3:Er3+ is assigned to the S-4(3/2) --> I-4(9/2) transition of Er3+ ions situated at the C-2 sites of cubic RE2O3 (RE = Y, Gd, Lu). The intensities of features in the 1.54 mum I-4(15/2)-I-4(13/2) absorption transition due to Er3+ at S-6 and C-2 sites are consistent with the site occupation ratio and the relative magnetic dipole-electric dipole intensity contributions of Er3+ at the different sites. The 1.54 mum emission lines are predominantly from Er3+ ions at C-2 sites. The different behaviours of the emission intensities 1.75 and 1.54 mum groups with change in Er3+ dopant ion concentration, preparation technique, Yb3+ co-doping, temperature change and different excitation line are rationalized. (C) 2004 Elsevier B.V. All rights reserved.