[Properties of energy transfer in two host materials doped with Ir(ppy)3 and Rubrene]

The devices with phosphorescent material tris(2-phenylpyridine)iridium [Ir(ppy)3] and fluorescent material 5,6,11, 12-tetraphenylnaphthacene [Rubrene] as dopants in two kinds of host were constructed in the present study. Respectively, the two kinds of host are polyvinylcarbazole [PVK] and 4,4'-N,N-dicarbazole-biphenyl [CBP]. We studied the properties of energy transfer between host materials and dopants. Firstly, the absorption and photoluminescence spectra of PVK, CBP, Ir(ppy)3 and Rubrene were measured. The spectral overlap between the photoluminescence of PVK and the absorption spectrum of Ir(ppy)3 is larger than that of Rubrene. The result of the spectral overlap for CBP is the same as PVK. It was shown that the energy transfer from the two host materials to Ir(ppy)3 is stronger than that to Rubrene. In addition, the energy transfer from Ir(ppy)3 to Rubrene is possible according to their absorption and photoluminescence spectra. We compared the electroluminescence properties of different devices. In devicel of ITO/PVK : Rubrene : Ir(ppy)3 (100 : 5 : x)/BCP(10 nm)/Alq3 (20 nm)/Al and device 2 ITO/CBP : Rubrene : Ir(ppy)3 (100 : 5 : x)/BCP(10 nm)/Alq3 (20 nm)/Al(x = 0, 3), under the same DC bias, the electroluminescence results show that energy transfer from host to Rubrene through Ir(ppy)3 is the main mechanism. And energy transfer is much more efficient in CBP as host than in PVK. In addition, at the same voltage, the light power of the device doped with Ir(ppy)3 and Rubrene is obviously stronger than that of the device doped with Rubrene only. When the concentration of Ir(ppy)3 increases, the light power decreases at the same voltage, and the effect of concentration quenching is enhanced.