What is the key factor affecting the cathodoluminescence intensity of europium complexes?

In order to substitute well-studied, but hard-to-deposit inorganic cathodoluminescent (CL) compounds with coordination compounds with organic ligands, its is primarily important to establish CL correlation to photoluminescence, as well as to increase the CL intensity. In the present paper it was studied for homo- and mixed-ligand 1,4-terephthalates and naphthalene-2,6-carboxylates of europium, including novel, for one of which (Eu2(nda)3(BPhen)2) the crystal structure was determined. They were found to display luminescence of various intensities under excitation by fast electrons, characteristic for Eu3+. CL intensity correlated with PLQY, when saturation regime was not reached, and with PLQY/τ in saturation regime.