Luminescence properties of pyrazolic 1,3-diketone Ho³⁺ complex with 1,10-phenanthroline

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 Ho³⁺ 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 Ho³⁺ 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 Ho³⁺ complex was developed. It was shown that the energy transfer from the excited triplet level of the ligand environment to the ⁵F₅ level of Ho³⁺ is responsible for the emission of the ion in the complex.