Judd-Ofelt analysis of dimeric europium carboxylates with gradually changing distortions of the crystal field around Eu3+3+ion

Experimental and theoretical Judd-Ofelt intensity parameters S2 lambda , rates of radiative Arad and nonradiative Anrad processes, and quantum efficiency of luminescence were calculated for a series of related aromatic and aliphatic carboxylates [Eu2(RCOO)6L2] (L - 1,10-phenanthroline or 2,2 '-bipyridine) using the LUMPAC software. The behavior of these characteristics in the sequence of europium carboxylates with the gradually changing distortions of the crystal field, which is mainly caused by variation in the bond lengths of the bridging-cyclic COOgroups with Eu3+ ion, was analyzed. A correlation between the changes in the value of the S22 intensity parameter, the radiative rate Arad, and the ratio of metal-ligand bond lengths in the Eu coordination polyhedron was demonstrated. The dependence of the parameter S22 on the distribution of metal-ligand orbital overlap among Eu-ligand bonds of the compound was revealed. The higher S22 values in the set of aromatic carboxylates are associated with a more distorted nearest environment of the Eu3+ ion which is caused by the influence of the bulky R fragments. It is shown that the intensity of f-f transitions of the Eu3+ ion in the compounds under investigation is determined foremost by the dynamic coupling (DC) mechanism. The contribution of this mechanism to the parameters S22 and S24 is close to 100 %, its contribution to the S26 parameter is 85-92 %. The luminescence quantum efficiency for the studied europium carboxylates varies in the range of 52-74 %.