Defect clustering in an Eu-doped NaMgF3 compound and its influence on luminescent properties

Abstract

Luminescent properties of compounds based on lanthanide ions are strongly influenced by defect clustering, and unfortunately, these defects are not fully understood in lanthanide-doped fluoroperovskite materials. In this context, we studied the structural properties and effects upon incorporation of divalent and trivalent Europium dopant ions in the orthorhombic phase of NaMgF₃, combining classic atomistic simulations and crystal field models. We developed a new set of interatomic potentials that reproduce the structural properties, as well as lattice parameters, interatomic distances and volumes, and elastic properties, with good accordance with experimental results. Analysis of the solution energy revealed that Eu³⁺ is most energetically favourable in the Mg site, while Eu²⁺ is most favourable in the Na site. The mechanism of charge compensation was investigated in both cases. We also analysed the local symmetry, charge transfer in Eu–F chemical bonding, crystal field parameters, and ⁷F₁ energy sub-levels of the Eu³⁺ ion in the host matrix based on crystal field and electronegativity models. In addition, we discussed the photoionization cross-section and optically stimulated luminescence (OSL) decay pattern for Eu²⁺-doped NaMgF₃. Thus, this work provides direction for new material design and opens up a framework to analyse structural and defect changes of fluroperovskite compounds upon lanthanide ion insertion.