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Measurements using positron annihilation lifetime (PALS) and Doppler broadening annihilation radiation lineshape (DBARLS) spectroscopies were performed in several lanthanide dipivaloylmethanate complexes, Ln(dpm) 3 where Ln = Sm 3+ , Gd 3+ , Tb 3+ , Ho 3+ , Er 3+ , Yb 3+ and dpm = 2,2,6,6-tetramethyl-3,5-pentanedionate, and also on their binary solid solutions and mechanical mixtures, biphasic systems, of the general formula Ln 1− x Eu x (dpm) 3 . Expressive positronium formation was observed in all Ln(dpm) 3 complexes, except in Eu(dpm) 3 complex. The results indicate formation of solid solutions in the Sm 3+ , Gd 3+ and Tb 3+ systems, where total inhibition of positronium formation was observed. A Stern–Volmer type equation, I 3 0 / I 3 = 1 + kx , was used to fit the data, enabling the calculation of the inhibition constants, k . A mechanical mixture behavior, with linear variation of I 3 between the I 3 values of the pure complexes, was observed in systems containing Ho 3+ , Er 3+ and Yb 3+ complexes, where no effective solid solution formation occurred due to differences between the crystalline structures of these complexes and Eu(dpm) 3 . No positronium quenching reactions were observed in the solid solutions. DBARLS results confirmed those of PALS, evidencing that the positron annihilation spectroscopies are useful techniques to characterize the formation of solid solutions. PALS measurements at 80 K were performed in the Sm 1− x Eu x (dpm) 3 and Gd 1− x Eu x (dpm) 3 solid solutions. The results indicate that, despite a contraction in the crystalline structures, the solid solution structure remains intact at low temperatures. The temperature dependence of the inhibition constant do not seem to be understood from the positronium formation spur model and might be related to intra and intermolecular energy and charge transfer processes in the solid solutions, which is currently being studied. |
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