Solid state photoluminescence studies of [EuLⁿH₂(NO₃)₃](H₂O)_x macrocyclic complexes with Schiff base ligands

Three Eu^III macrocyclic complexes [EuLⁿH₂(NO₃)₃](H₂O)_x based on the ligands derived from 2-hydroxy-5-methyl-1,3-benzenedicarbaldehyde and three different amines: o-phenylenediamine, Eu-OPDA; ethylenediamine, Eu-EDA; and 1,3-diaminopropane, Eu-DAP have been synthesized via a metal template reaction. Eu-EDA and Eu-DAP showed metal based emission; for the Eu-OPDA complex these luminescent properties were not observed. From the photoluminescence emission measurements from ~13 to 300 K, the R/O = I (⁵D₀ → ⁷F₂)/I (⁵D₀ → ⁷F₁) ratio, together with two intensity parameters (Ω₂ and Ω₄), radiative lifetimes (τ_R) and branching ratios (β_{0 J′}) were calculated based on the Judd-Ofelt theory, for Eu-EDA and Eu-DAP. While the behavior of these parameters for the Eu-DAP complex is temperature dependent, these remain constant for Eu-EDA. The temperature dependence observed for the Eu-DAP complex indicates that for temperatures below 120 K, the local symmetry of the Eu^III center is modified, as compared to the environment of the same metal center at room temperature.