Theoretical spectroscopic investigation of the Eu3+ local symmetry in LiF through crystal field models

Abstract

We employed the simple overlap model (SOM) with the method of equivalent nearest neighbours (MENN) in the Auzel-Malta equation and in the energy sublevels equations to investigate the local symmetry of the Eu3+ in the LiF crystal and predict the 7F1, 7F2 and 5D1 energy sublevels. The Batista-Longo Improved Model (BLIM) was helpful to predict the Eu3+ ion charge and establish the Eu–F interaction charge position considering the covalence on the chemical bonding by the Brik-Avram overlap integrals matching with the octet rule. The LiF:Eu3+ were studied elsewhere in two situations. In the first case, the Eu3+ occupies a site without inversion centre because the 5D0 – 7F2 (0-2) transition is more intense than 5D0 – 7F1 (0-1) transition, which we indicate spectral behaviour of the a α-EuF3 polymorphic phase. Thus, with a combination of non-null crystal field parameters, we obtained the luminescent site as being a distorted C2v symmetry with charge factors g1 = 0.485, g2 = 0.499, g3 = 0.403, g4 = 0.343 and g5 = 0.257. This set of charge factors reproduced the 7F1 manifold in good agreement with experimental data. In the second case, with the 0-1 transition more intense than the 0-2 transition, we have the indication which the Eu3+ occupies a site with distorted inversion centre. Furthermore, due to the asymmetry of the peaks, we performed a deconvolution of these peaks with two lines in both 7F1 and 7F2 manifolds. Assuming the distorted luminescent site have being D4h or D4d symmetries with g = 0.383 and D2d symmetry with g1 = 0.400 and g2 = 0.396, we have reproduced satisfactory the 7F1 level splitting and 7F2 and 5D1 sublevel positions, considering the Eu3+ octacoordinated.