A study of the ligand composition change of the Eu$^{3+}$ chelate by two-stage laser excitation luminescence and computer simulation of kinetics

The europium(III)–tris(dibenzoylmethane)–triphenylphosphine oxide complex was studied in the polycrystalline state and in toluene at 298 K using the luminescence excitation method with two-stage rectangular pulses with decreasing intensity of stages. Experimental nonmonotonic kinetic curves were numerically simulated within the framework of a four-level dynamic model describing reversible processes in the complex, associated with its structural rearrangement. The maximum correspondence between the experimental and simulated curves was obtained using an iterative approximation performed using the Nelder–Mead algorithm. Based on the obtained numerical values of the rate constants and parameters of the model, experimental kinetics were interpreted, and it was concluded that they are a consequence of the processes associated with changes in the ligand composition of the Eu$^{3+}$ chelate.