Optical properties of Er 3+ in fullerenes and in β-PbF 2 single-crystals

Abstract

With the aim of providing a thorough description of the optical properties of Er 3+-doped endohedral fullerenes, we studied their characteristics in the light of those of well-known Er 3+-doped β-PbF 2 single-crystals. Various Er 3+-doped endohedral fullerenes were considered: Er 2C 2@C 82, where the Er 2C 2 group is encapsulated inside a cage of 82 carbon atoms and the Er 3− x Sc x N@C 80 ( x = 0, 1 and 2) family, where the Er 3N, Er 2ScN and ErSc 2N clusters are trapped in a 80 carbon atom cage. In this article, we discuss the absorption and photoluminescence of trivalent erbium ions in fullerenes and in β-PbF 2 crystals. The extinction coefficient of Er 3N@C 80 was found to be 4.8 (±0.5) × 10 3 mol/l −1 cm −1 at 540 nm, due to the C 80 cage absorbance. Even in a saturated fullerene solution, the absorption of Er 3+ encapsulated inside a C 80 cage cannot be observed at room temperature. We suggest that this is due to an insufficient number of Er 3+ ions in the solution and their low absorption cross-section. Low temperature photoluminescence measurements show that the line width of Er 3+ in a carbon cage, dissolved in a polycrystalline solvent, is similar to the one of Er 3+ in β-PbF 2 single-crystals. The quantum efficiency of Er 3+ at 1.5 μm in fullerenes is four orders of magnitude lower than that for Er 3+ in crystals, due to very efficient non-radiative decay processes. Molecular vibrations of the cage might be responsible for those rapid non-radiative de-excitations.