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Project ID: G5RD-CT-2001-00577
Finanziato nell'ambito di: FP5-GROWTH
Paese: Belgium

Development of novel lanthanide complexes, especially sandwich type and perhalogenated sandwich type erbium complexes, for IR LED applications

The Leuven group has been (and still is) mainly involved in synthesis and screening of novel lanthanide complexes. Up till now, a whole range of compounds has been developed, including novel quinolinate, betadiketonate, sulfonyl imide and other complexes of mainly erbium, neodymium and ytterbium ions for NIR applications.

In inorganic waveguides, the erbium ion shows 1.53µm emissions with very long luminescence lifetime. This feature, along with the luminescence quantum yield close to 1, lead to very efficient optical amplification. However, the transfer of these properties in an all organic device is difficult. Organic molecules have harmonics of vibration close to 1.5µm, and the excited erbium level can couple to the vibrations and allow efficient non-radiative transfers to take place, which explain the shorter luminescence lifetime and lower luminescence quantum yield. As a result, the population inversion threshold in such materials is very high (estimated to be 930mW for an erbium doped polymer with 0.8µs luminescence lifetime).

To overcome these problems, it is possible to use an energy transfer from the ligand to the lanthanide ion, using the very intense absorption transition of the organic part of the complex. Since ligands are often rather simple organic molecules, their main absorption band lies in the UV to blue part of the electromagnetic spectrum, a region where commercially available pumping diodes are expensive. For luminescence in the near-infrared, it is interesting to push further the absorption of the ligand into the red, where pumping diodes are commercially available. We chose tetra tert-butyl phthalocyanine, for its high absorption cross section in the red. The structure of the erbium phthalocyanine was characterized using mass spectroscopy (MALDI-TOF), and the characteristic lifetimes of the singlet, triplet and erbium states were measured, along with the branching ratios and therefore the sensitisation efficiency.

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Rik VAN DEUN, (Senior Scientist)
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