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Lanthanides in Luminescent Thermometry Chapter 281 389 molecular demultiplexer. This opens the possibility of using this molecular thermometer in medical- and biotechnologies, such as blood diagnostics, “lab-on-a-molecule” systems, and molecular computational identification of small objects (de Silva, 2011). 5.2.1 In Polymer Matrices Early examples of luminescent thermometers based on Ln3+ complexes embedded into polymer matrices comprise emission intensity variations of single-center emitters. However, one of the first examples studied the influ- ence of ligands, polymers, and complex/polymer ratio using both decay life- time and intensity variation (278–323 K) as the thermometric parameters (Khalil et al., 2004). The ligands were b-diketonates with different aromatic and fluorinated substituents, see Fig. 20. One of the ligands was tta that has an aromatic heterocycle linked to the diketonate group and a strong electron withdrawal group (–CF3) that increases the ionicity of the ligand. Another ligand was F7 that has several electron withdrawal groups and therefore a stronger interaction with the metal (high Lewis acidity), but it does not have any aromatic ring. Other ligands employed in this comparative study were D2, with a high aromatic area, and 3p-hfb, with both an aromatic and electron withdrawal residues. Finally, they also used N-based bidentate ligands, as phen or bphen, to increase the coordination number of the b-diketonate com- plexes from 3 to 4. The different polymers were fluoroacrylic polymer, poly- carbonate, and Teflon®. The loading of the complexes in the polymer was also varied between 1/10 and 1/600 ratios. The higher aromaticity of D2 in com- parison with tta had the effect of shifting the excitation maximum from 350 to 400 nm. A high number of aromatic cycles in the ligands were also enhanc- ing the maximum Sa values, which decreased from 4.42%K1, for [Eu(D2)3(phen)] complexes, to 0.9%K1, for [Eu(F7)3] ones; corresponding to Sm values, computed by us, of 1.77% K1 and 0.82% K1, respectively. Increasing the coordination number from tris to tetrakis was not beneficial due to the intensity photodegradation (from 7.2% to 16.2% intensity lost per hour of irradiation), despite the slightly increase of the maximum Sa values, from 2.27%K1 to 2.40%K1, corresponding to Sm values, computed by us, of 1.82% K1 and 1.49% K1, respectively. Whereas Sr increased with the concentration (up to 1/10), the relative sensitivity based on lifetime values was higher for the lowest concentration (1/600). The role of the polymer is obviously to provide the desired physical and chemical properties to the ther- mometer for a given application, but is also acting on the thermometric per- formance. In this case, the sensitivity in fluoroacrylic polymer was the highest followed close by polycarbonate and decreasing 4 in Teflon. The thermometer was formulated as paint prepared by dispersion in dichloro- methane or trifluorotoluene. The paint was sprayed or spin coated onto alumi- num or glass substrates (Khalil et al., 2004).PDF Image | HANDBOOK ON THE PHYSICS AND CHEMISTRY OF RARE EARTHS
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