With the development of organic light-emitting diodes, interests in themechanisms of charge carrier photo generation, separation, transport andrecombination continue to grow. Phosphorescent organic light-emitting diodes havegained considerable interest in the last 10 years because of high luminanceefficiency. In the present paper, the authors investigated the optical andelectrical characteristics of the devices based on Ir(ppy)3 and Ir(piq)3 dopedPVK matrix emission layer at room temperature. The PL spectra show that theenergy transfer from PVK to Ir(piq)3 is harder than that of PVK to Ir(ppy)3. TheLuminescence characteristics of devices with different doping ratio show that itis not the energy transfer from matrix, but the recombination of injectedcarriers on phosphorescent molecules that is the main origin of EL emissions.From the viewpoint of energy level, the characteristics of carrier-trap andtransport in Ir(piq)3 are better than in Ir(ppy)3 due to the high HOMO and lowLUMO in Ir(piq)3.基金项目(20090009110027, 20070004024), 博士点新教师基金项目(20070004031), 北京市科技新星计划项目(2007A024), 北京市自然科学基金项目(1102028)和中埃科技合作联委会中方项目(5-Ⅲ-19)资助