The effect of temperature on the luminescent properties of terbium-europium complexes with N-heterocyclic ligands
Bozhko A.A.., Kharcheva A.V., Borisova N.E., Ivanov A.V., Patsaeva S.V., Lomonosov Moscow State University
Abstract
The study of rare-earth element complexes is a task of particular importance as they have a wide field of applications due to their outstanding properties. For example, they may be used as molecular thermometers, OLED components or chemical sensors. The presence of several rare-earth element ions in the complex can increase the sensitivity of the solution to external changes, therefore, the registration of luminescence spectra of such complexes under various experimental conditions is crucial. In this work, we measured the absorption, emission, and luminescence excitation spectra of rare earth element complexes with potential polytopic N-heterocyclic ligands in the simultaneous presence of two emitting centers (europium + terbium) in the temperature range from 20 to 60°C with a various ratio of the ligand, europium ions, and terbium ions in solution. The temperature dependences of the spectral characteristics were obtained, including the luminescence lifetime, the quantum yield of luminescence. Differences in the behavior of different complexes with increasing temperature and changing the ratio of ion concentrations were also evaluated. It was found that the lifetime of phosphorescence does not depend either on temperature or on the ratio of the concentration of ligand and ions. The phosphorescence excitation spectra differ in shape for the terbium and europium ions incorporated in the complex. The integral luminescence intensities of the europium complex increase when heated, and the dependences are monotonous and almost linear. An increase in the concentration of europium in solution leads to an increase in the luminescence of europium and a decrease in the luminescence of terbium. The irreversibility of changes in the emission and excitation spectra of luminescence after cooling of solutions to initial temperature was also detected. The possible mechanisms of temperature effects on luminescent properties are discussed.
Speaker
Bozhko Alena
Lomonosov Moscow State University
Russia
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