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Two new Sm 3+ complexes with pyrazolic β-diketones bearing a CF 3 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 Sm 3+ 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 Sm 3+ 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., (Copyright © 2019 Elsevier B.V. All rights reserved.)

We performed spectroscopic investigations of a novel tris(1,3-bis(1,3-dimethyl-1H-pyrazol-4-yl)propane-1,3-dionato)(1,10-phenanthroline) holmium (III) complex. It was demonstrated that bonding the corresponding ligand environment to Ho 3+ results in sensitization of the luminescence of the complex. The luminescence decay of the complex exhibits a biexponential behaviour. The short-lived component is attributed to the fluorescence of the ligand, whereas the long-lived component is connected with the Ho 3+ emission. Using fluorescence lifetime imaging, it was shown that there is a single type of emission sites in the studied complex. Based on the results of the optical measurements, the energy diagram for the investigated Ho 3+ complex was developed. It was shown that the energy transfer from the excited triplet level of the ligand environment to the 5 F 5 level of Ho 3+ is responsible for the emission of the ion in the complex., (Copyright © 2019 Elsevier B.V. All rights reserved.)