Primarily White

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Science  11 Feb 2005:
Vol. 307, Issue 5711, pp. 819
DOI: 10.1126/science.307.5711.819a

For organic light-emitting devices (OLEDs), white light emission has been achieved through the complex and tailored fabrication of multilayer devices either by evaporative or spin coating deposition, or by the blending of two blue-light emitters whose interactions give rise to an exciplex state. In all of these cases, the purity of the white light depends on the quality and concentration of the various species, and generally is a function of the applied voltage.

Mazzeo et al. have fabricated an OLED that requires only a single layer of material to generate white light by using an oligothiophene compound. As single molecules in solution, this compound has an intrinsic blue-green emission, whereas in the solid phase, it also produces a red-shifted emission, as crosslinked dimers form. Optical measurements on thiophene compounds that did not form dimers did not show a red-shifted emission spectrum. When wired into a device, the oligothiophene showed electroluminescent emission spectra similar to its photoluminescence, but with a more intense red-shifted peak, leading to the emission of white light (superposed blue-green and red emissions). The intensity of the output in air was similar to that of the best multilayer OLEDs, indicating that this material may find use in general lighting applications. — MSL

Adv. Mater. 17, 34 (2005).

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