Local structure of molybdates solid solutions containing europium by results of atomistic simulation

Abstract

Atomistic modeling of europium-containing scheelite-like molybdates promising for use in solid-state lighting is performed. The analysis of local structure of the nearest environment of europium ion in the powellite-based solid solutions, namely Ca2(MoO4)2 – Eu2(MoO4)3 and Ca2(MoO4)2 – NaEu(MoO4)2, has been accomplished. The similar analysis was also performed for solid solutions based on double molybdates of both stoichiometric NaGd(MoO4)2 – NaEu(MoO4)2 and cation-deficient Na2Gd4(MoO4)7 – Na2Eu4(MoO4)7 compositions. The comparison of the local structures has been implemented at equal content of europium replaced ∼ 5% of “calcium” sites.It is shown that the symmetry of the cation site occupied by europium in all the studied solid solutions decreases compared to the symmetry of this site in the scheelite structure. The nearest distance between the europium ions is 3.90–4.01 Å. It is shown that the multivariate environment of the activator ion in the double molybdates causes a strong dispersion of interatomic distances Eu-O. It is found that these changes lead to a strong distortion of the oxygen polyhedra EuO8 holding the relative proximity of their average size. The latter circumstance may explain the observed by spectroscopic studies the existence of single center of europium in these complex systems.