Evidence of the participation of electronic excited states in the mechanism of positronium formation in substitutional Tb1−xEux(dpm)3 solid solutions studied by optical and positron annihilation spectroscopies

Abstract

Positronium formation in the bimary molecular solid solutions Tb_1−xEu_x (dpm)₃ (dpm = dipivaloylmethanate) has been investigated. A strong linear correlation between the ⁵D₄ Tb(III) energy level excited state lifetime and the positronium formation probability has been observed. This correlation indicates that the ligand-to-metal charge transfer LMCT states act in both luminescence quenching and positronium formation inhibition, as previously proposed. A kinetic mechanism is proposed to explain this correlation and shows that excited electronic states have a very important role in the positronium formation mechanism.