Effect of ancillary ligands on visible and NIR luminescence of Sm³⁺ -diketonate complexes

Two new Sm3+ complexes with pyrazolic beta-diketones bearing a CF3 group acting as main ligands and with 2,2'-bipyridine or 1,10-phenanthroline being the ancillary ligand were studied, and their energy level structure was established. Stark splitting observed in the photoluminescence spectra of the complexes points to their non-cubic symmetry, confirmed by the calculated Judd-Ofelt intensity parameters. Internal quantum yields obtained for the compounds by the Judd-Ofelt calculations were of the order of 5.5%, whereas the measured external quantum yields were 0.75% and 1.5% for Sm3+ complexes involving 2,2'-bipyridine and 1,10-phenanthroline ancillary ligands, respectively, with the corresponding sensitization efficiencies calculated as 0.16 and 0.26. It was demonstrated that replacing the 1,10-phenanthroline ancillary ligand with 2,2'-bipyridine provides an increase in the intensity of 650 nm emission of the Sm3+ complexes, with the branching ratio reaching 55%. Intensive emission of the studied complexes at 650 nm offers hope for their use as spectrally pure red emitters. (C) 2019 Elsevier B.V. All rights reserved.