Luminescence and positron spectroscopies studies of Eu3+ complexes containing tris(2,2,6,6-tetramethyl-3,5-heptanedionate) and 2-pyrrolidone as ligands

This work is reports the luminescent properties and positronium formation yields of the Eu(dpm)3 and Eu(dpm)3(2-pyr) complexes, where dpm = 2,2,6,6-tetramethyl-3,5-heptanedionato (dipivaloylmethanate) ion and 2-pyr = 2-pyrrodilidone. We present and discuss experimental intensity parameters of 4f-4f transitions in the Eu3+ complexes under UV excitation. Positron annihilation lifetime spectroscopy (PALS) and Doppler broadening of annihilation radiation lineshape (DBARL) measurements were also performed. It was observed that the photoluminescent properties and Ps formation yields of the complexes are related to intramolecular processes, such as a ligand-to-metal charge transfer (LMCT). The results, which strongly evidence the participation of molecular excited states in the positronium formation, were then discussed in terms of the recently proposed Ps formation mechanism, named cybotactic correlated system kinetic mechanism (CCSKM).