In-situ luminescence analysis of coordination sensors (ILACS): Looking inside chemical reactions
Many modern technologies depend on the discovery of materials with new or improved properties, which are usually solid compounds.Unfortunately, the synthesis of these materials is still mostly developed by chance. Although a very large number of effective methods are available today, almost all synthesis approaches have a basic principle in common, in which certain reactants are brought to react and, only in the end of the reaction, the often randomly formed products are characterized. For developing strategies for a rational synthesis of solids or for discovering entirely new compounds, processes such as nucleation, crystal growth or formation of intermediates must be examined in detail during the reactions. Because these intermediates can be stable or metastable and rapidly convert to other phases, conventional ex-situ methods are not suitable. Therefore, many very efficient methods such as X-ray diffraction, X-ray spectroscopy, nuclear magnetic resonance, infrared and Raman spectroscopy have been used for in-situ monitoring of chemical reactions in the past few years. However, besides many advantages, these methods have also grave disadvantages as for instance with regard to the detection limit, temporal resolution, availability or type of substances to be investigated. One method that could provide additional information as well as overcome the above-mentioned disadvantages of the available characterization methods, is the in-situ luminescence analysis of coordination sensors (ILACS, Fig. 1)  applying high-resolution CCD detectors (Fig. 2). Within this approach, emitting coordination sensors as the lanthanide ions Eu3+, Eu2+, Ce3+[3-6] are introduced into the system under examination and monitored with the aid of in-situ luminescence under real reaction conditions. Since the luminescence of these ions are highly dependent on the coordination environment, this method provides information about the changes in the coordination number, bond lengths, covalence of the ligands and symmetry of the cation site during chemical reactions. This procedure is easily available, is characterized by high sensitivity and high temporal resolution and can also be used for studying very small crystallites or amorphous materials. Hence, the aim of this project is to develop a new in-situ characterization method and to test its performance for different reaction systems as Eu(phen)2(NO3)3, Eu,Tb,Ce(bipy)2(NO3)3 (phen = 1,10-phenanthroline, bipy = 2,2’-bipyridine) as well as more complex compounds as doped calcium phosphate phases.
Fig. 1. ILACS principle: Coordination sensors introduced to reaction system. Structural changes during formation of solids monitored by in-situ luminescence measurements.
|Fig. 2. Adaptation of the in-situ crystallization cell at the University of Kiel for the ILACS experiments. (Photo source: Marvin Radke).|
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