Cathodoluminescence from organic bilayer induced by field electron emission of carbon nanotubes

We report the observation and studies of cathodoluminescence (CL) of organic bilayer structures, such as tris-(8-hydroxyquinoline) aluminium (Alq3) and 2-tert-butylphenyl-5-biphenyl-1,3,4-oxadiazole (PBD) deposited on ITO-coated glass, with and without hole transport layer, N,N′-diphenyl-N,N′-bis(1-naphthyl)-(1,1′-phenyl)-4,4′-diamine (α-NPD). To excite the CL of such bilayer organic heterostructure, low energy electrons field emitted by single walled carbon nanotube cathodes were utilized. The dependence of CL spectrum and intensity on voltage (V), current (I), type of transport layer and the cathode-anode geometry has been studied. We propose carbon nanotubes as efficient cathodes for stable CL emission from organic multilayer heterostructures. The role of both electron and hole transport layers on stability and spectrum of CL is also discussed.