OLEDs based on Ln(III) complexes for near-infrared emission

Abstract The development of organic light-emitting diodes in the near-infrared range aims to take advantage of the opportunities that arise from plastic electronics: lightweight and large-area panels at low cost, eventually on flexible substrates. New applications, such as in signaling without visual contamination, night vision, or security, along with biomedical, therapeutic applications or solid-state lighting in greenhouses, offer an important commercial niche. In this chapter, particular attention is paid to the unique properties associated with the use of lanthanide compounds (narrow spectral bandwidths, good efficiency, stability, and possibility of reaching wavelengths >900 nm) and to their comparison with other approaches targeted also at the generation of infrared emission. The emitting properties of Ln(III) complexes depend on the variety of ligands that may be employed, whose electronic levels must meet certain conditions, which are reviewed. Their integration into electroluminescent devices adds even more requirements related to charge transport and manipulation. The general problems encountered, various classical solutions (host-guest strategies), and some novel approaches are reviewed.