Layered Double Hydroxides as a Matrix for Luminescent Rare Earth Complexes
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Layered Double Hydroxides as a Matrix for Luminescent Rare Earth Complexes Natalia G. Zhuravleva1, Andrei A. Eliseev1, Alexey V. Lukashin1, Ulrich Kynast2, Yuri D. Tretyakov1 1 Materials Science Department, Moscow State University, Moscow 119992, Russia 2 Department of Chemical Engineering, Muenster University of Applied Science, 48565 Steinfurt, Germany ABSTRACT In the present work new luminescent materials with high quantum efficiencies based on layered double hydroxides (LDH) were obtained. Intercalation of complexes into the interlayer space of LDH doesn’t affect their luminescent properties, forming non-volatile solid state material with good optical properties. The Coulomb interactions between LDH layers and complex can result in a change of complex structure in comparison with free complexes and in decreasing the number of the organic ligands per Ln atom. The energy transfer in the system was also studied. INTRODUCTION The synthesis and investigation of new luminescent materials combining excellent optical characteristics with physical and chemical stability is one of the important problems in modern material science [1-3]. The development of novel synthetic methods for the preparation of such materials usually involves combination of optical elements with stability of solid state matrices. In the present study we report synthesis of luminescent materials based on molecular complexes of Tb and Eu rare earths (RE) intercalated into the interlayer space of layered double hydroxides (LDH). Cheap and available magnesium-aluminum LDHs are known as a very convenient matrices for intercalation of different chemical compounds [4]. Optical transparency, chemical and photochemical stability of these matrices enables their possible application for preparation of various optical materials [5]. Besides the ability to control the quantity of complex intercalated and homogeneous distribution of anions in the interlayer space make LDH matrices very attractive for intercalation of different functional molecules in comparison with previously used zeolites and sol-gel matrixes. Moreover, intercalation of complexes into the interlayer space allows to investigate the structure and properties of complex in spatially constrained twodimensional system of cavities, while the controlling the complex quantity of to adjust RE-RE distance. To determine the influence of the corresponding confinement on luminescent efficiency and energy transfer within the layers we performed synthesis of terbium and europium picolinate (pyridine-2-carboxilate, “pic”) complexes embedded into layered double hydroxides with different Tb/Eu ratios. EXPERIMENTAL DETAILS The series of MgnAl(OH)2n+2[Ln(pic)4·mH2O] samples with different terbium to europium ratio (Ln = Tb, Eu, Tb0.98Eu0.02, Tb0.9Eu0.1, Tb0.5Eu0.5) were synthesized. Mg-Al LDHs in carbonate form were obtained by co-precipitation of magnesium and aluminum nitrates
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(Mg2+:Al3+ = 2:1, 3:1, 4:1, 6:1, 9:1, 12:1) by the mixture of NaOH and Na2CO3 at pH = 10,0±0,1. [6]. To enhance the c
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