Evidences of the participation of excited states in the positronium formation mechanism in Sm1-xEux(dpm)3 and Gd1-xEux(dpm)3 solid solutions

Positron annihilation lifetime (PALS) and optical spectroscopies measurements were performed in Sm3+, Eu3+ and Gd3+ dipivaloylmethanate complexes, Ln(dpm)3 (dpm = 2,2,6,6-tetramethyl-3,5-pentanedionate), and also on their binary solid solutions of general formula Ln1-xEux(dpm)3, where Ln = Sm3+ or Gd3+. The results indicate that photophysical processes present in the solid solutions, such as a ligand-to-metal charge transfer (LMCT), and Sm3+  Eu3+ energy transfers, are strongly related to the positronium (Ps) formation probability. The results were interpreted from a kinetic model involving the participation of excited states in the Ps formation that we are calling correlated cybotactic system kinetic mechanism (CCSKM).