Study On Luminescence Characteristics Of Blue Phosphorescent FIrpic

In1997, Forster et al found phosphorescent electroluminescent phenomenon which broke the theory limit25%of the organic light-emitting diodes (OLEDs) quantum efficiency and made the development of organic electroluminescent into a new period. Organic phosphorescent electroluminescent have made huge progress both in theory and device efficiency after more than ten years’development. During the course, iridium complexes is a kind of high efficient phosphorescent materials that widely studied. Phosphorescent OLEDs (PhOLEDs) usually use doping structure as emitting layer (EML) to avoid the negative effect such as concentration quenches, and the doping ratio of the host materials and the object materials has an important impact to the emitting characteristics of the devices. Usually, the methods to further improve the performance of the devices are using low power function materials as the cathode, introducing hole/electron transport materials (HTL/ETL) in the devices structure and annealing treatment, et al. Among these methods, annealing treatment has the superiorities that operation simple, process concise, application wide and effect obvious.The blue-ray iridium complex electrophosphorescent materials (bis[2-(4,6-difluoropheny1)pyridy1-N,C2] iridium (Ⅲ)(FIrpic) was used as object material, the high polymer Poly(9-vinylcarbazole (PVK) and small molecular materials4,4’-bis(9-carbazoly1) bipheny1(CBP) which the triplet state energy level higher than FIrpic were used as host materials in this paper. The FIrpic solution with different concentrations and FIrpic:PVK/FIrpic:CBP mixture solution with different ratio were made up to research the photoluminescence (PL) characteristics of the films prepared from different solutions. The experimental results show that the PL spectra of FIrpic prepared from the solution with different concentrations have three emitting peaks at about476,500and530nm, the relative intensity of the emitting peaks were changed along with the concentration chang of FIrpic (the thickness of film). In the same preparation conditions (speed, the amount of spin coating solution), when the concentration of FIrpic was up, the intensity of the emitting peak at about476nm is continue to decrease while the emitting peak at about530nm is continue to increase and the whole spectra has a redshift trend; the films shown a greenish-yellow light. In the subject and object of doping system, the emitting of FIrpic at about530nm was obviously restrained when the PVK doping ratio was up. When the ratio of FIrpic:PVK was less than8%, there only two emitting peaks at476and500nm, showing a blue light. In the FIrpic:CBP doping system, the PL characteristics has the similar regular pattern.The influence of doping ratio and annealing treatment to the emitting charactristics of FIrpic was researched in the paper. The emitting color of the films with different doping ratios and the PhOLEDs accordingly was changing from blue to greenish-yellow with the FIrpic doping ratio up. The absorption and PL spectrua has an apparent overlap in the440-480nm range, the intensity decrase of emitting at about476nm along with the FIrpic doping ratio increase was due to the self-absorption of FIrpic. Measuring the EL and PL spectra under differenr stimulate density, the intensity of emitting peak at abou530nm was increase along with the simulate density increases which confirmed that the emitting at about530nm was excimer emitting.The change of EL specra before and after annealing treatment further confirmed that the annealing treatment could promote the FIrpic molecular gathered and the radiaton transiton emitting between the FIrpic molecules. After optimizing the devices structure and annealing treatment, the high brightness PhOLEDs whose emitting color turned from blue to yellow-green were obtained.