Dual emission tunable in the near-infrared (NIR) and visible (VIS) spectral range by mix-LnMOF†
In this study, we describe the synthetic approach, crystallographic structure, luminescent behavior and elucidation of the channels of the energy conversion in heteronuclear coordination polymers with emission in the visible (Eu3+ and organic ligand) and near-infrared (Nd3+) range. The [(Nd0.9Eu0.1)2(dipc)3(H2O)3]n·nH2O, [(Nd0.7Eu0.3)2(dipc)3(H2O)3]n·nH2O, [(Nd0.5Eu0.5)2(dipc)3(H2O)3]n·nH2O, [(Nd0.3Eu0.7)2(dipc)3(H2O)3]n·nH2O, [(Nd0.1Eu0.9)2(dipc)3(H2O)3]n·nH2O, [Eu2(dipc)3(H2O)3]n·nH2O and [Nd2(dipc)3(H2O)3]n·nH2O materials are obtained by hydrothermal conditions from pyridine-2,6-dicarboxylic acid (H2dipc) and Ln2O3 oxide (Ln = Eu and Nd). The fine structures in the emission spectrum and spectral profile are used to investigate the ion responsible for the emission characteristics of a material (6), based on coordination polyhedron. The heteronuclear systems show emission in the dual spectral range (NIR-VIS) tuned for blue or red. The tuning of emission on the red (Eu3+) or blue (organic ligand) range may be performed by controlling the stoichiometric ratio of the lanthanide ions and by controlling the excitation wavelength. Nd3+ ions display self-absorption of emission to dipc ligand, resulting in interference on the emission band profile ranging from 400 to 600 nm. The energetic process of energy transfer is operated by a cascade of energy transfer, from dipc ligand mainly to Eu3+ ions and finishing on the Nd3+ ion. The efficient sensitization to Nd3+ by Eu3+ ions is due to the presence of many resonant energy levels and the short distance between these ions.