Photoluminescence quantum yield of pure and molecularly doped organic solid films

We present measurements of the absolute photoluminescence (PL) quantum yiel d, phi(PL), for a wide variety of organic compounds in solid films, pure an d molecularly doped with strongly fluorescent materials. The procedure, whi ch uses an integrating sphere, does not entail comparison to other standard s, and provides accurate measure of the photoluminescence efficiency for su bmicron thick films, prepared by high vacuum vapor deposition. Host materia ls include N,N'-diphenyl-N,N'-bis(3-methylphenyl)-1,1'-biphenyl-4-4'-diamin e (TPD), a common hole transport material for light emitting diodes, tris ( 8-hydroxyquinolinolato) aluminum (III) (Alq(3)) and its methyl derivative, Almq(3), two aluminum chelates used as electron transport and/or green emit ting materials. Dopants include tetraphenylnapthacene (rubrene) and N,N'-di ethyl quinacridone (DEQ). Doping results in a substantial increase (similar to a factor 2-4) of phi(PL) in comparison with that of the pure host. For instance, measured phi(PL) increases from 0.25 and 0.42 for pure Alq(3) and Almq(3), respectively, to near unity upon doping with rubrene at a concent ration of similar to 1 mol %. The above data are discussed within the frame work of Forster energy transfer from host to guest. (C) 1999 American Insti tute of Physics. [S0021-8979(99)03017-0].