Synthesis, structural modelling and luminescence of a novel erbium(III) complex with 2,4-nonanedione and 2,2 0 -bipyridine ligands for chitosan matrices doping P. Martín-Ramos a,b,⇑ , P. Chamorro-Posada c , M. Ramos Silva b , P.S. Pereira da Silva b , I.R. Martín d , F. Lahoz d , V. Lavín d , J. Martín-Gil a a Advanced Materials Laboratory, ETSIIAA, Universidad de Valladolid, Avda. Madrid 44, 34004 Palencia, Spain b CEMDRX, Physics Department, Universidade de Coimbra, Rua Larga, P-3004-516 Coimbra, Portugal c Signal Theory Department, ETSIT, Universidad de Valladolid, Paseo Belén 15, 47011 Valladolid, Spain d Department of Physics and MALTA Consolider Team, Universidad de La Laguna, E-38200 San Cristóbal de La Laguna, Santa Cruz de Tenerife, Spain article info Article history: Available online 28 October 2014 Keywords: Erbium(III) b-Diketonate Photoluminescence Chitosan abstract We report the synthesis, the Sparkle/PM7 semi-empirical quantum model for the ground state geometry and the absorption/luminescent properties of the Er 3+ ternary complex [Er(nd) 3 (bipy)] (where Hnd is 2,4-nonanedione and bipy is 2,2 0 -bipyridine). The solid-state electronic absorption spectra and the photoluminescent spectra show long-wavelength 4f–4f transitions which provide a potential use of the compound as a NIR-emitting material for the doping of polymer-based matrices for waveguides or for bio-analytical applications. The dispersion of the novel complex in a biocompatible chitosan film has been assessed. Ó 2014 Elsevier B.V. All rights reserved. 1. Introduction Er 3+ -based light conversion molecular devices (LCMDs) have applications in the generation (emitting materials in OLEDs) and amplification of light (EDFAs) in the C-band transmission window for fiber-optic communications [1–5], in solar energy conversion [6–8] and in sensory technology [9,10]. Further, NIR emission has been reported to have advantages for biological applications in terms of medical imaging resolution, detection sensitivity and transmittance of the tissues, as noted by Sun et al. [11]. LCMDs’ electronic and photophysical properties strongly depend on the control of the coordination sphere of the optically active rare earth ion. Particular attention has to be paid to the design of the ligands, which sensitize the Er 3+ ion by antenna effect and shield it from quenching effects. The efficiency of this sensiti- zation process depends critically on the distance between the ion and the sensitizer: the antenna chromophore needs to be in close contact with the lanthanide to ensure efficient transfer. Thus, both the knowledge of the structural data and the study of the lumines- cent properties are essential in order to develop materials with improved luminescence efficiency. With regard to hybrid materials (host:guest systems), there is a growing realization of the importance of combining aforemen- tioned functional materials with low-cost, environmentally- friendly biopolymers. The natural, biodegradable and biocompati- ble chitosan is one the most promising candidates, due to its ability to form films, transparency, non-toxicity, excellent adsorption fea- tures, etc. [12]. Several examples of Eu 3+ -doped chitosan or chito- san–silica hybrids have been reported in the literature [13–15] and the suitability of chitosan for optical planar nano-patterned waveguides has been confirmed by Yoon et al. [16]. This work presents the synthesis and structural modelling by semi-empirical calculations of a novel highly-coordinated Er 3+ b- diketonate complex. Its properties have been investigated by Fou- rier Transform infrared (FTIR) spectroscopy, Raman spectroscopy, calorimetry and photoluminescence spectroscopy. Finally, we report the preparation and optical characterization of a chitosan film doped with this material, in a preliminary effort for the design and elaboration of a material suitable for optical architectures or biomedical applications. 2. Experimental 2.1. Physical and optical measurements C, H, N elemental analysis was made using a Perkin Elmer CHN 2400 apparatus. Differential scanning calorimetry (DSC) data were http://dx.doi.org/10.1016/j.optmat.2014.09.036 0925-3467/Ó 2014 Elsevier B.V. All rights reserved. ⇑ Corresponding author at: Advanced Materials Laboratory, ETSIIAA, Universidad de Valladolid, Avda. Madrid 44, 34004 Palencia, Spain. Tel.: +34 979108347. E-mail address: pablomartinramos@gmail.com (P. Martín-Ramos). Optical Materials 41 (2015) 139–142 Contents lists available at ScienceDirect Optical Materials journal homepage: www.elsevier.com/locate/optmat