Materials Science Forum, Vol.517, 173-182, 2006
Photoluminescence processes in the triplet state of phosphorescent organic materials : Ir(ppy)(3) doped in TPD
Photoluminescence (PL) measurements have been made for a spin-coated thin film of phosphorescent tris(2-phenylpyridine) iridium [Ir(PPY)(3)] doped in N,N'-bis (3-methylphenyl)-N, N'-bis(phenyl)-benzidine (TPD) host material in the temperature range from 10 K to room temperature. When temperature is increased from 10 K to 300 K, the PL intensity of Ir(PPY)(3) increases from 10 K and decreases above about 200 K. Theoretical calculations are undertaken for the temperature dependence using (1) a three-level model where three zero-field splitting substates are generated in the triplet state of Ir(PPY)(3) and (2) endothermic energy transfer from the TPD host to the Ir(ppy)(3) guest, and (3) energy diffusion from the excited TPD to the neighboring unexcited TPD. A good agreement was obtained between the measured and calculated temperature dependences of the PL intensity.