Organic electroluminescent devices are light-emitting diodes in which the active materials consist entirely of organic materials. Here, the fabrication of a white light-emitting organic electroluminescent device made from vacuum-deposited organic thin films is reported. In this device, three emitter layers with different carrier transport properties, each emitting blue, green, or red light, are used to generate white light. Bright white light, over 2000 candelas per square meter, nearly as bright as a fluorescent lamp, was successfully obtained at low drive voltages such as 15 to 16 volts. The applications of such a device include paper-thin light sources, which are particularly useful for places that require lightweight illumination devices, such as in aircraft and space shuttles. Other uses are a backlight for liquid crystal display as well as full color displays, achieved by combining the emitters with micropatterned color filters.

White-light-emitting organic electroluminescent devices with multilayer structures were fabricated using lanthanide metal complexes as the emitter layers. A device with a structure of glass substrate/indium-tin oxide/tetraphenyldiamine derivative (TPD)/terbium complex (tris(acetylacetonato)(monophenanthroline)Tb(III))/ europium complex (tris(dibenzoylmethanato)(monophenanthroline)Eu(III))/aluminum complex (Alq)/Mg:Ag exhibited white electroluminescence. The spectrum consisted of three discrete peaks at 410–420 nm, 545 nm, and 615 nm, from TPD, Tb complex, and Eu complex, respectively.

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We have examined the valence-band electronic structures of gold and silver in the same column in the periodic table with nominally filled d orbitals by means of a recently developed polarizationdependent hard x-ray photoemission. Contrary to a common expectation, it is found that the 5d-orbital electrons contribute prominently to the conduction electrons in gold while the conduction electrons in silver are to some extent free-electron-like with negligible 4d contribution, which could be related to a well-known fact that gold is more stable than silver in air. The 4d electron correlation effects are found to be essential for the conduction electron character in silver.

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