Materials of the International Seminar of the Institute of Spectroscopy of the Russian Academy of Sciences (ISAN), dedicated to the anniversary of Professor M.N. Popova
Spectroscopy of condensed state

Role of LMCT states in luminescence excitation processes in europium indolecarboxylates

V. I. Tsaryuk, K. P. Zhuravlev

Fryazino Branch, Kotel’nikov Institute of Radio Engineering and Electronics, Russian Academy of Sciences, Fryazino, Moscow oblast, Russia

Abstract: The luminescence excitation energy transfer in europium and terbium indole-3-carboxylates, indole-3-acetates and indole-3-propionates as well as ternary indolecarboxylates containing 1,10-phenanthroline and 2,2'-bipyridine molecules have been studied. The luminescence excitation spectra, the lifetimes of the $^5D_0$ (Eu$^{3+}$) and $^5D_4$ (Tb$^{3+}$) states, and the luminescence intensity are analyzed. The decisive role of ligand-metal charge transfer (LMCT) states in the quenching of the luminescence of europium aromatic carboxylates containing a $\pi$-excessive pyrrole or indole fragment is demonstrated. Most europium compounds are characterized by quenching due to the depopulation of the $^5D_0$ state of the Eu$^{3+}$ ion through the low-energy LMCT state. But in some ternary compounds, the LMCT state being of higher energy participates in the nonradiative depopulation of the excited electronic states of the ligand.

Keywords: luminescence, Eu$^{3+}$, Tb$^{3+}$, LMCT, indolecarboxylate, $\pi$-excessive heterocycle.

Received: 30.06.2021
Revised: 30.06.2021
Accepted: 14.07.2021

DOI: 10.21883/OS.2022.01.51899.26-21

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