PHOTOLUMINESCENCE AND STRUCTURE OF FULLERITE C_(60) INTERCALATED WITH HELIUM

摘要

Powder x-ray diffractometry was employed to study infusion of He into C_(60) fullerite. It has been shown that the intercalation at a pressure of 0.1 MPa is a two-stage process, the first stage being the saturation of the octahedral voids, virtually complete after 55 hr. Photoluminescence spectra have been measured at 5 K on C_(60) with virtually completely saturated octahedral voids. Helium in the lattice voids is shown to reduce that part of the luminescent emission which is due to 0-0 transitions around 1.69 eV from the so-called deep traps, or according to existing notions, covalently bound pairs of C_(60) molecules. The effect of intercalation with helium on dimer formation in fullerite C_(60) is ascribed to a combined action of the following factors: intercalation-related changes of the pentagon to hexagon configuration ratio, formation of a bonded state of He in the C_(60) lattice, and moderation by helium of the orientational phase transition near 260 K, the last factor resulting in a reduced number of dislocations (which also promotes dimer formation).