WHITE-LIGHT AND RED-GREEN-BLUE (RGB)ELECTROLUMINESCENCE BY LIGHT COLOR-CONVERSION

We present methods which provide color-conversion of light emission fr om organic LED's using a multilayer structure. for the purpose of spec tral color control. These devices with multicolor emission are suitabl e for applications in flat panel color display technology. The LED's p roduced using an active layer of para-hexa-phenyl (PHP, a bright. stab le source of blue light as a pump source can be efficiently combined w ith color-converting layers consisting of green (Coumarin) and red (Lu mogen F300) dyes in PMMA matrices. By controlling the absorption and r eflection mechanisms of multilayer device structures we an able to dem onstrate the production of multicolor light (RGB emission) and in addi tion. the color-mixing required to produce white light. By designing t he color-converting films with a specific thickness or concentration o f the dye (thus tailoring the optical density of the converter layers) , the spectral emission can thus be controlled. By investigating the c olor-conversion process in a multilayer stack RGB device, a method of maximizing the brightness by improved coupling between the multilayers is presented. (C) 1998 Elsevier Science B.V.