Emission tuning study of RGB blends. Interaction of two EL polymers and a red dye

A study of light emission in photo- and electroluminescence in blends composed of a blue and a green emitting polymers with a red dye was performed. To gain information about the tunability of the RGB mixture, the blends varied in composition. The polymers were poly(2,7-9,9′-dihexylfluorenediyl) (blue), poly(9,9-di-hexylfluorenediyl divinylene-alt-1,4-phenylenevinylene) (green) and the dye was 4-(dicyanomethylene)-2-methyl-6-(dimethylaminostyryl)-4H-pyrane (red).It was verified that in photoluminescence Forster type energy transfer plays the main role in the emission. In solution a large concentration of the acceptors is needed to attain the transfer radii, whereas in the solid state, the transfer is very sensitive to small variations in the acceptor content, with large changes in emission spectra. The band gaps of the components allowed a cascade energy transfer mechanism. In electroluminescence, apart from the energy transfer mechanism, an important role is played by the trapping of charge carriers, resulting in significant differences between the PL and EL spectra.