Temperature Changes in Luminescence of Mixed Complexes of Terbium and Samarium with Organic Ligands Based on 2,2\({}^{\boldsymbol{\prime}}\)-bipyridylcarboxamides

Solutions in acetonitrile of three mixed complexes of rare-earth elements (terbium and samarium) with organic ligands with various pyridine substituents were studied in this work. The ratios of ligands and metals in the resulting complexes were determined, and the stability constants of samarium complexes were calculated using the spectrophotometric titration method. Measurements of absorption-, emission-, and excitation spectra of luminescence, luminescence kinetics of solutions of mixed complexes of rare-earth elements with an excess of metal relative to the ligand were carried out at various temperatures in the range 298–328 K. For the first time, an increase of luminescence intensity of a samarium ion in complex upon heating was observed. The dependences of the luminescence quantum yield and lifetime of mixed complexes on temperature were obtained. A thermometric parameter—the ratio of the integral luminescence intensities of samarium and terbium ions—was proposed, and the temperature sensitivity coefficient of this parameter was determined for different complexes.