Temperature dependence of phosphorescence intensity and lifetime of tris(2-phenylpyridine) iridium doped in the fluorescent material TDP

Abstract

Numerical calculation has been undertaken on the temperature dependence of photoluminescence (PL) intensity and PL lifetime of fac tris(2-phenylpyridine) iridium $[\mathrm{Ir}{(\mathrm{ppy})}_{3}]$ phosphorescent material doped in $4,{4}^{\ensuremath{'}}$-bis[N-(p-tolyl)-N-phenyl-amino]biphenyl (TPD) and compared with the experimental result. We use a model in which three zero-field splitting substates 1, 2, and 3 of the lowest-energy metal-to-ligand--charge-transfer triplet states are responsible for the phosphorescence, together with the lowest-energy triplet state of TPD (level 4) at $645\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$ below the lowest triplet substate 1 of $\mathrm{Ir}{(\mathrm{ppy})}_{3}$. We assume the nonradiative one-phonon relaxation is undertaken among these four levels. A good agreement is obtained between the temperature dependence of the observed and calculated PL intensities and lifetimes.