Near-infrared electroluminescence and stimulated emission from semiconducting nonconjugated polymer thin films

We present the results of a study on near-infrared electroluminescence and optical amplification in semiconductor thin films based on a nonconjugated polymer doped with luminescent and electron-transport molecules. A single-layer light-emitting diode is fabricated on an indium tin oxide-coated glass substrate with poly(9-vinylcarbazole) containing an electron-transport material, 2-(4-Biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole and a near-infrared-emitting compound, 2-(6-(p-dimethylaminophenyl)-2,4-neopentylene-1,3,5-hexatrienyl)-3-ethylbenzothiazolium perchlorate. The single-layer structure shows near-infrared electroluminescence with a turn-on voltage of 13 V. The same structure is characterized under transversal pulsed photopumping with a frequency-doubled Nd: yttrium aluminum garnet laser. With increasing pump fluence, the edge emission at 0.82 mu m shows both significant gain narrowing and superlinear intensity increase, which indicate the existence of optical gain by stimulated emission. Our results provide impetus for the development of near-infrared polymer lasers and optical amplifiers.