Electroluminescence rare-earth -diketonates

From the first synthesis of rare-earth /9-diketonates in 1897 by Urbain until now, hundreds of different complexes formed by reaction between Lnni ions and /3-diketone derivatives have been described in the literature. Interest for this type of complexes comes from then-potential application in numerous and diverse domains. These complexes can be used for example as extractants in solvent-solvent extraction processes or as active compounds for the development of chelate lasers or liquid lasers. But they can also find applications in NMR as shift reagents or as electroluminescent materials in organic light-emitting diodes (OLEDs) (Binnemans, 2005b). 

One of the most interesting features observed in OLEDs based on RE + diketonate complexes is the presence of electrophosphorescence (EP). This phenomenon occurs in electroluminescent devices when the emission arises from a T state. It is noted that the emitted color by this device depends on the ratio between the rare-earth EL sharp peaks and the EP broad emission band from the T S transition of the tta ligand. An advantage of this system is that it can be used to obtain different colors by simply changing the applied voltage. 

Lanthanide p-diketonates are amongst the best smdied rare-earth luminescent complexes [58]. They are brightly luminescent and volatile so that incorporation into various electroluminescent materials is simple. Moreover their photophysical properties are easily tuned by a judicious choice of ancillary ligands. Indeed, conventional synthesis usually yields bis(hydrated) lanthanide tris(P-diketonates), but the two solvent molecules can be substituted by either a fourth diketonate anion or a donor ligand with adequate functionalisation as to provide convenient light harvesting and subsequent energy transfer onto the metal ion. It is noteworthy that not only visible but also near-infrared luminescence [59,60] is efficiently sensitised in lanthanide p-diketonates. In the case of Eu , some ternary complexes have quantum yields up to 85% [8] and the main asset of their luminescent properties is an emission essentially concentrated in the hypersensitive Dq transition... 

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