Switchable ErSc2N rotor within a C80 fullerene cage:

An EPR and photoluminescence excitation study

John J. L. Morton,1, 2, _ Archana Tiwari,1 Geraldine Dantelle,1 Kyriakos Porfyrakis,1 Arzhang Ardavan,2 and G. Andrew D. Briggs1 1Department of Materials, Oxford University, Oxford OX1 3PH, United Kingdom 2Clarendon Laboratory, Department of Physics, Oxford University, Oxford OX1 3PU, United Kingdom

(Dated: February 8, 2008)

Systems exhibiting both spin and orbital degrees of freedom, of which Er3+ is one, can o_er mechanisms for manipulating and measuring spin states via optical excitations. Motivated by the possibility of observing photoluminescence and electron paramagnetic resonance from the same species located within a fullerene molecule, we initiated an EPR study of Er3+ in ErSc2N@C80. Two orientations of the ErSc2N rotor within the C80 fullerene are observed in EPR, consistent with earlier studies using photoluminescence excitation (PLE) spectroscopy. For some crystal _eld orientations, electron spin relaxation is driven by an Orbach process via the _rst excited electronic state of the 4I15=2 multiplet. We observe a change in the relative populations of the two ErSc2N con_gurations upon the application of 532 nm illuminations, and are thus able to switch the majority

cage symmetry. This photoisomerisation, observable by both EPR and PLE, is metastable, lasting many hours at 20 K.