Abstract
Red organic electroluminescent (EL) devices based on tris(8-hydroxyquinorine aluminum) (Alq$_3$) doped with red emissive materials, 4-(dicyanomethylene)-2-t-butyl -6-(l,1,7,7-tetramethyljulolidyl-9-enyl)4H-pyran (DCJTB). poly(3-hexylthiophene) (P3HT). rubrene and 4-dicyanomethylene-2-methyl-6[2-(2,3.6.7-tetrahydro-lH,5H-benzo-[i,j]quinolizin-8yl)vinyl]-4H-pyran (DCM2) were fabricated for applying to the red light source, The photoluminescence (pL) intensities of red emissive materials doped in Alq$_3$ are limited by the concentration quenching with increasing the doping ratio and the doping concentration of DCJTB, DCM2, P3HT and rubrene measured at the maximum intensity showed 5, 1, 0.5 and 2 wt%, respectively. Time-resolved PL dynamic results showed that the PL lifetime of red emissive materials doped in Alq$_3$ were increased more than the value of material itself. It means that the efficient energy transfer occurred in the mixed state and Alq$_3$ is a suitable host materials for red emissive materials, The device which was used DCJTB as a dopant achieved the best result of the maximum luminance of 594 cd/$m^2$ at 15 V and showed the chromaticity coordinates of x=0,624, y=0,371.