Fluorescence spectroscopy and emission lifetimes of Er 3 in Er x Sc 3x N@C 80 x  1±3 R.M. Macfarlane a, * , D. S Bethune a , S. Stevenson b,1 , H.C. Dorn b a IBM Almaden Research Center, 650 Harry Road, San Jose, CA 95120-6099, USA b Department of Chemistry, Virginia Tech, Blacksburg, VA 24061, USA Received 3 April 2001; in ®nal form 7 May 2001 Abstract We have measured the spectra and lifetimes of the emission near 1.5 lm from Er 3 ions within the recently dis- covered endohedral metallofullerene family Er x Sc 3x N@C 80 . These molecules consist of a highly symmetric C 80 I h ) fullerene cage containing a triangular tri-metal nitride group. The measured emission decay lifetimes, the ®rst reported for ions in endohedral fullerenes, are all in the range 1.1±1.6 s, showing that for the present species the quantum ef- ®ciency for emission is 10 4 . High-resolution emission spectra at 1.6 K show sharp features that dier for the Er 1 ,Er 2 andEr 3 speciesandprovideinformationaboutthestructuraldierencesamongthem. Ó 2001ElsevierScienceB.V.All rights reserved. 1. Introduction We report the spectra and lifetimes of the 1.5 lm emission from Er 3 ions within the recently discovered endohedral metallofullerene family Er x Sc 3x N@C 80 . For the Sc 3 molecule, Sc 3 N@C 80 , NMR spectroscopy and X-ray crystallography have shown that the C 80 cage has I h symmetry [1]. This highly symmetric cage has just two types of inequivalent carbons ± 60 atoms make up 12 pentagonal rings and 20, on the molecular 3-fold axes, each link three pentagons together. The cage contains a planar triangular Sc 3 N group in which Er can substitute for any of the Sc to give a set of four molecules of the form Er x Sc 3x N@C 80 x  0±3;seeFig.1).AnX-raydiractionstudy[2] con®rming this picture has been reported for ErSc 2 N@C 80 . Early H uckel molecular orbital cal- culations indicated that the I h C 80 cage would be greatly stabilized by the addition of six electrons [3], a result noted by Yeretzian et al. in proposing that this cage was likely to be the predominant isomer for the La 2 @C 80 species they had produced [4]. The present molecules can thus be formally thought of as triangular M 3 N 6 groups inside C 6 80 cages. The dominant production of a single high-symmetry cage isomer for the entire Er x Sc 3x N@C 80 family, together with the avail- ability of all of the family members with x  0±3, makes this an important system for studying the interactions between the cage and the internal ions and interactions between the internal ions them- selves. Furthermore, these interactions take place in relative isolation since the carbon cages 3 August 2001 Chemical Physics Letters 343 2001) 229±234 www.elsevier.com/locate/cplett * Corresponding author. Fax: +1-408-927-2100. E-mail address: macfarla@almaden.ibm.com R.M. Mac- farlane). 1 Present address: Luna nanoMaterials, 2851 Commerce Street, Blacksburg, VA 24062, USA. 0009-2614/01/$ - see front matter Ó 2001 Elsevier Science B.V. All rights reserved. PII:S0009-261401)00701-1