Effects of Progressive Halogen Substitution on the Photoluminescence Properties of an Erbium-Porphyrin Complex

We have investigated the photoluminescence properties of porphyrin-based erbium and gadolinium complexes at different levels of halogen substitution. Both the intensity and the decay time of the erbium near-infrared emission correlate with the degree of the halogenation. Conversely, no clear correlation is found with the triplet-state energy levels nor with the intensity of the residual visible emission. Such findings confirm that the key role ill the low efficiency of the near-infrared emission is played by the nonradiative quenching of the erbium emitting level due to the vibrational modes of the surrounding C-H bonds.