Organic White Light-Emitting Diodes Using Fluorescent and Phosphorescent Materials for Color Tunable Devices

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First, we investigated the transient characteristics of poly(9,9-dioctylfluorene) (PFO)-based polymer OLEDs (PLEDs) doped with green emissive phosphor fac-tris(2-phenylpyridine)iridium(III) [Ir(ppy)_3] and red emissive phosphor tris(1-phenylisoquinoline)iridium(III) [Ir(piq)_3] by applying the voltage pulse on the devices, and achieved the maximum luminance of 4800 cd/m^2 and the ideal white emission with the Commission Internationale de L'Eclairage (CIE) coordinates of (0.33, 0.35) at the pulse width and frequency of 100 ns and 1 kHz, respectively. Especially, the CIE coordinates can be tuned from (0.25, 0.29) to (0.51, 0.40) by varying pulse width and frequency. Second, we investigated white OLEDs with blue emissive phosphor bis[(4,6-difluorophenyl)-pyridinato-N, C^2] (picolinate)iridium(III) (Flrpic) and some red emissive materials. Using Flrpic and red emissive rare earth complex of tris(divenzoylmethane)-mono(4,7-dimethylphenanthroline)europium(III) [Eu(dbm)_3phen] doped in poly(N-vinylcarbazole)(PVK), the white emission of (0.31, 0.38) in the CIE coordinates was obtained at a current density of 0.5 mA/cm^2. Utilizing the different transient characteristics between the host and dopant, emission color has been successfully tuned by varying the applied pulse width and frequency.
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