Platinum Metals Rev., 2002, 46, (4), 187
Electrically Induced Phosphorescence
When the voltage applied to a poly(para -phenylene) ladder-type polymer being tested for LED use was switched off, a team of researchers in Germany and Austria (J. M. Lupton, A. Pogantsch, T. Piok, E. J. W. List, S. Patil and U. Scherf, Phys. Rev. Lett., 2002, 89, (16), 167401) saw a long-lasting pink phosphorescent glow (λ ~ 600 nm) instead of the expected, but shorter lasting, blue-green fluorescence (λ ~ 450 nm). Very low concentrations (~ 80 ppm) of Pd atoms left over from the process catalyst and bound to the polymer backbone are thought to be responsible for this new effect.
Large numbers of dark long-lived triplet states generated in the polymer by the electrical excitation may diffuse thermally through the polymer film until they encounter a Pd site where they decay as phosphorescence.