New chelate complexes of trivalent Y and lanthanides (Eu, Ho, Yb) with a triazene N-oxide: Synthesis, structural characterization and luminescence properties

► Synthesis and X-ray characterization of new triazene N-oxide lanthanide complexes. ► Luminescent and optical properties of a triazene-oxide europium complex. ► HOMO-LUMO and triplet state energy calculations (ligand). ► Theoretical and experimental ground state geometries for [Eu{O2N(C6H4)NNN(O)Ph}4]. ► Energy levels diagram for the ligand (triplet state) and europium(III). ► Emission spectra of [Eu{O2NPhNNN(O)Ph}4] with λex = 365 nm.