Evidence of Anionic Disorder in Fluoride Borate Eu3(BO3)2F3 from Eu3+ Luminescence: Comparison with Fluoride Carbonate Ba2Eu(CO3)2F3

The optical behavior of europium fluoride borate Eu3(BO3)2F3 and barium fluoride carbonates Ba2Eu(CO3)2F3 is investigated with Eu3+ as a local structural probe. Tentative correlation between the optical and structural data are discussed. Unexpected broad emission lines are observed for Eu3+ in fluoride borate and the separation of two crystallographic sites, predicted from the structure determination, is impossible. It is assumed that deviation from the ideal stoichiometry Eu3(BO3)2F3 occurs and is due to the substitution BO3-33F-, leading to the formulation Eu3(BO3)2+xF3-3x. Crystal field analysis is performed on the 7FJ basis of the 4f6 configuration of Eu3+. The crystal field parameters (cfp) and crystal field strength parameter NV are similar for both compounds though slightly larger for Eu3(BO3)2F3 This difference is especially significant for two rank (cfp), indicative of a larger electrostatic field in Eu3(BO3)2F3.