Near-infrared electroluminescence of polymer light-emitting diodes doped with a lissamine-sensitized Nd3+ complex

We report 890 nm luminescence from a neodymium-doped polymer light-emitting diode. The active layer is a blend of poly(dioctylfluorene-co-benzothiadiazole), F8BT, and a lissamine-functionalized terphenyl-based neodymium complex. We detect electroluminescence from both the lissamine (580 nm) and the Nd3+ complex (890 nm). By comparison with lissamine-free devices we show that the lissamine is crucial to infrared emission. The neodymium/lissamine luminescence intensity ratio is higher under electrical excitation than under optical excitation, showing that more triplets reach Nd3+ under electrical excitation. High turn-on voltages provide a clear indication for charge trapping onto the lissamine, and we consider direct triplet formation on the lissamine to be competing efficiently with respect to slower Dexter-type triplet transfer from the F8BT to the lissamine. (C) 2001 American Institute of Physics.