Enhanced 1520 nm photoluminescence from Er³⁺ Ions in di-erbium-carbide metallofullerenes (Er₂C₂)@C₈₂ (Isomers I, II, and III)

Di-erbium and di-erbium-carbide endohedral metallofullerenes with a C ₈₂ cage such as Er₂@C₈₂ (isomers I, II, and III) and (Er₂C₂)@C₈₂ (isomers I, II, and III) have been synthesized and chromatographically isolated (99%). The structures of Er₂@C₈₂ (I, II, III) and (Er₂C ₂)@C₈₂ (I, II, III) metallofullerenes are characterized by comparison with the UV-vis-NIR absorption spectra of (Y₂C ₂)@C₈₂ (I, II, III), where molecular symmetries of the structures are determined to be C_s, C_2v and C _3v, respectively. Furthermore, enhanced near-infrared photoluminescence (PL) at 1520 nm from Er³⁺ ions in Er ₂@C₈₂ (I, III) and (Er₂C₂)@C ₈₂ (I, III) have been observed at room temperature. The PL intensities have been shown to depend on the symmetry of the C₈₂ cage. In particular, the PL intensity of (Er₂C₂)@C ₈₂ (III) has been the strongest among the isomers of Er ₂@C₈₂ and (Er₂C₂)@C₈₂. Optical measurements indicate that the PL properties of Er₂@C ₈₂ (I, II, III) and (Er₂C₂)@C₈₂ (I, II, III) correlate strongly with the absorbance at 1520 nm and the HOMO-LUMO energy gap of the C₈₂ cage.