Electroluminescence
Electroluminescence(EL) is an optical phenomenon and electrical phenomenon in which a material emits light in response to the passage of an electric current or to a strong electric field. This is distinct from black body light emission resulting from heat (incandescence), from a chemical reaction (chemiluminescence), sound (sonoluminescence), or other mechanical action (mechanoluminescence).
Electroluminescence is the result of radiative recombination of electrons and holes in a material, usually a semiconductor. The excited electrons release their energy as photons - light. Prior to recombination, electrons and holes may be separated either by doping the material to form a p-n junction (in semiconductor electroluminescent devices such as LEDs), or through excitation by impact of high-energy electrons accelerated by a strong electric field (as with the phosphors in electroluminescent displays).
(Wikipedia; Electroluminescence, 4/13/2011)
Electrically conducting polymers have been used in a variety of organic electronic devices, including in the development of electroluminescent ("EL") devices for use in light emissive displays. With respect to EL devices, such as organic light emitting diodes (OLEDs) containing conducting polymers, such devices generally have the following configuration: anode/buffer layer/EL material/cathode The anode is typically any material that is transparent and has the ability to inject holes into the EL material, such as, for example, indium/tin oxide (ITO). The anode is optionally supported on a glass or plastic substrate. EL materials include fluorescent dyes, fluorescent and phosphorescent metal complexes, conjugated polymers, and mixtures thereof. The cathode is typically any material (such as, e.g., Ca or Ba) that has the ability to inject electrons into the EL material.
The buffer layer is typically an electrically conducting polymer and facilitates the injection of holes from the anode into the EL material layer. The buffer layer can also be called a hole-injection layer, a hole transport layer, or may be characterized as part of a bilayer anode. Typical conducting polymers employed as buffer layers include polyaniline ("PAni") and polydioxythiophenes such as poly(3,4-ethylenedioxythiophene) ("PEDT"). These materials can be prepared by polymerizing aniline or dioxythiophene monomers in aqueous solution in the presence of a water soluble polymeric acid, such as poly(styrenesulfonic acid) ("PSSA"), or poly(2-acrylamido-2-methyl-1-propanesulfonic acid) ("PAAMPSA"), as described in, for example, U.S. Pat. No. 5,300,575 and published PCT application WO 02/065484. A well known PEDT/PSS material is Baytron.RTM.-P, commercially available from H. C. Starck, GmbH (Leverkusen, Germany).
Recent US Patents
11/23/2010
7,837,902
Compositions of electrically conductive polymers and non-polymeric fluorinated organic acids
Hsu, Harmer and Junk of DuPont, Delaware has produced a conductive material for an electroluminescent material consisting of a conductive polymer and a non-polymeric fluorinated organic acid, wherein the conductive polymer is selected from a polythiophene, a polypyrrole or a polyaniline. (RDC 4/8/2011)
Recent Journal Articles
Luminescent properties of long-lasting BaAlxOy:Eu2+,Dy3+ nanocomposites
(243–252)Journal of Applied Polymer Science 121 #1 (2011)
Bern et al of the University of the Free State and Kenyatta University, South Africa, added different volume fractions of the BaAlxOy:Eu2+,Dy3+ powder to LDPE polymer. The LDPE-phosphor interface did not significantly change the spectral positions of the phosphor materials, whose major emission peaks occurred at about 505 nm. The improved afterglow results for the composites may have been caused by morphological changes due to increased surface area and defects. Thermal results indicate that the BaAlxOy:Eu2+,Dy3+ particles acted as nucleating centers and enhanced the overall crystallinity in the LDPE nanocomposite while preventing lamellar growth, hence reducing the crystallite sizes in LDPE. (RDC 4/14/2011)
New deep blue light emitting copolymer containing fluorene, carbazole, and dialkoxynaphthalene
(43–48)Journal of Applied Polymer Science 121 #1 (2011)
Teh et al of the Universiti Kebangsaan, Malaysia, used conducting emeraldine salt (PANI-ES) and intrinsic leucoemeraldine polyaniline (PANI-LEB) in the synthesis of DGEBA-grafted PANI via anionic copolymerization. Results obtained indicated that the graft copolymer exhibited higher electrical and thermal conductivities than that of the blend counterpart. (RDC 4/14/2011)
New deep blue light emitting copolymer containing fluorene, carbazole, and dialkoxynaphthalene
(43–48)Journal of Applied Polymer Science 121 #1 (2011)
Teh et al of the Universiti Kebangsaan, Malaysia, used conducting emeraldine salt (PANI-ES) and intrinsic leucoemeraldine polyaniline (PANI-LEB) in the synthesis of DGEBA-grafted PANI via anionic copolymerization. Results obtained indicated that the graft copolymer exhibited higher electrical and thermal conductivities than that of the blend counterpart. (RDC 4/14/2011)