Crystal structure and luminescence of complexes of Eu(III) and Tb(III) with furan-2,5-dicarboxylate Sebastiaan Akerboom a , Wen Tian Fu a , Martin Lutz b , Elisabeth Bouwman a,⇑ a Leiden Institute of Chemistry, Gorlaeus Laboratories, Leiden University, P.O. Box 9502, 2300 RA Leiden, The Netherlands b Crystal and Structural Chemistry, Bijvoet Center for Biomolecular Research, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands article info Article history: Received 6 December 2011 Accepted 26 January 2012 Available online 1 February 2012 Keywords: Lanthanide Luminescence Sensitization Furan-2,5-dicarboxylate abstract Four new Ln(III) complexes (Ln = Eu, Tb) with furan-2,5-dicarboxylic acid (H 2 FDA) as a ligand have been synthesized and characterized in the solid state. Luminescence studies indicate that the compounds exhi- bit line-like luminescence characteristic of the lanthanide centre upon excitation in the ligand absorption bands. Single crystal X-ray diffraction study of {[Eu(FDA)(H 2 O) 5 ]½(FDA)3H 2 O} n shows the formation of an inorganic polymer with infinite Eu-FDA chains. Ó 2012 Elsevier B.V. All rights reserved. 1. Introduction The invention of the InGaN Light Emitting Diode (LED) chip, emitting in the near UV and blue spectral region, has created new possibilities for replacing the current sources of artificial light with more energy efficient ones [1]. Conventional incandescent and fluo- rescent lamps rely either on thermal emission or on gas discharge followed by energy down conversion by phosphors. Both of them result, however, in significant energy losses due to the high temper- ature and large stokes shifts [2]. On the other hand, LEDs convert electric energy into light directly and they are more efficient. How- ever, the emission of LEDs is intrinsically monochromatic. The cur- rent technology of fabricating white LEDs makes use of a blue LED chip, emitting in the 450–480 nm range, to excite a yellow phosphor or a mixture of green and red phosphors. Alternatively, white LEDs can be obtained by using a near UV-LED chip, to pump red, green and blue phosphors. Both approaches require phosphor materials, and the development of new materials is highly required [3]. Phosphors are widely used in modern day technology such as fluorescent tubes, X-ray photodetectors and plasma display panels [4–6]. Nearly all phosphor materials developed for these applica- tions are inorganic oxides. The key advantages of oxide materials are their high stability and high luminescence efficiency. However, they suffer from several disadvantages that make them relatively expensive. Firstly, the preparation of oxide materials requires high temperatures, typically around 1500 °C, resulting in a costly manufacturing process. Secondly, the rare earth dopants and host materials should have a high purity (4 N) to reduce non-radiative losses. For instance, the presence of only 5 ppm of Fe will reduce the quantum efficiency of Y 2 O 3 :Eu by as much as 7% [7]. Thirdly, the recycling of rare earths from oxide materials is difficult due to the relatively complicated chemical process and a profitable method is still to be found [8]. A class of compounds that might just overcome these draw- backs is the one of lanthanide coordination complexes. As discov- ered in 1942 by Weissman, the ligands in these compounds can act as an antenna that absorbs incoming radiation and transfers it sub- sequently to the lanthanide ion [9]. The favorable luminescent characteristics of the lanthanides, such as millisecond lifetime and line like emission, are therefore retained in these compounds [10]. Unlike the oxide-based phosphors, the preparation of com- plexes can be carried out at much lower temperatures, usually less than 200 °C. This can significantly reduce the production costs. In addition, complexes are molecule-based solid materials. They do not require highly pure rare earths as starting materials. Further- more, recycling the expensive rare earths can be easily achieved from complexes, e.g. by dissolution in inorganic acids or by burn- ing. Besides these advantages, the absorption properties of com- plexes can be, in principle, designed to match the excitation source by modifying the ligands. Ligands that are known to be good antennae for the lanthanide ions include b-diketonates [11– 13], Schiff bases [14,15], macrocycles [16,17] and aromatic carbox- ylates [18–20]. Recent work in our group has shown that pyridine- 2,6-dicarboxamide is able to sensitize both Eu 3+ and Tb 3+ centred luminescence efficiently [21]. In subsequent work, it was found that the structurally similar pyridine-2,6-dicarboxylate is a suit- able antenna for both Eu 3+ and Tb 3+ complexes with quantum 0020-1693/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.ica.2012.01.053 ⇑ Corresponding author. Tel.: +31 71 5274550; fax: +31 71 5274761. E-mail address: bouwman@chem.leidenuniv.nl (E. Bouwman). Inorganica Chimica Acta 387 (2012) 289–293 Contents lists available at SciVerse ScienceDirect Inorganica Chimica Acta journal homepage: www.elsevier.com/locate/ica