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27 August 2003 Excited state properties of C60 revisited: a Raman study
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The excited state properties of C60 thin films have been probed in the temperature range 77-273K using Raman spectroscopy. The change in the Raman pentagonal pinch mode of C60 (whose position is largely independent of temperature) was monitored as a function of the excitation intensity at 514.5nm. This mode, normally positioned at 1469cm-1, was seen to shift reversibly to a lower Raman frequency with increasing laser intensity. Two excited state species have been identified. The first, at 1466cm-1 has been associated with the molecular triplet of C60 as determined from measurements preformed in solution. The second species at 1463cm-1, has been speculated to be an excited state co-operative involving two or more excited states in the solid and is seen to be intrinsic to solid state C60 below the phase transition, as similar measurements in solution show no Raman evolution beyond 1466cm-1. This species observed at 1463cm-1 has previously been reported in the depolymerisation of solid state C60, as well as in reversible processes in C60 crystals and has been characterised by a nonlinear photo-luminescence and photoconductivity. It is further proposed in this study that this excited state is analogous to a number of highly conducting states recently reported for C60. The data presented highlights the existence of a highly non-linear delocalised excited state species at low temperatures which is intrinsic to solid state C60.
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Gordon Chambers, Siobhan Bridget Phelan, Garrett F. Farrell, Alan Brian Dalton, and Hugh James Byrne "Excited state properties of C60 revisited: a Raman study", Proc. SPIE 4876, Opto-Ireland 2002: Optics and Photonics Technologies and Applications, (27 August 2003);

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