Acuminated fluorescence of centres in endohedral fullerenes through the incarceration of a carbide cluster

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 Er 2 C 2 @ C 82 (isomer I). The characteristic emission in the 1.5–1.6 μm region corresponds to the 4 I 13 / 2 ( m ) → 4 I 15 / 2 ( n ) transitions of the Er 3 + ion for both molecules. The emission arising from Er 2 C 2 @ C 82 ( I ) appears acuminated (narrow lines that taper to a point) when compared with that of Er 2 @ C 82 ( I ) . The Er 2 C 2 @ C 82 ( I ) emission linewidths are comparable to those found in crystals, making this molecule of interest for applications where accessible, well-defined quantum states are required.