Photoluminescence spectroscopic measurements have allowed the acquisition of high resolution spectra at low temperature for the endohedral metallofullerenes, Er-2@C-82 (isomer I) and Er2C2@C-82 (isomer I). The characteristic emission in the 1.5-1.6 mu m region corresponds to the I-4(13/2) (m) -> I-4(15/2) (n) transitions of the Er3+ ion for both molecules. The emission arising from Er2C2@C-82 (I) appears acuminated (narrow lines that taper to a point) when compared with that of Er-2@C-82 (I). The Er2C2@C-82 (I) emission line-widths are comparable to those found in crystals, making this molecule of interest for applications where accessible, well-defined quantum states are required. (C) 2009 Elsevier B.V. All rights reserved.