Special Features of Photo- and Electroluminescence of Zinc and Magnesium Complexes
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Russian Physics Journal, Vol. 63, No. 8, December, 2020 (Russian Original No. 8, August, 2020)
SPECIAL FEATURES OF PHOTO- AND ELECTROLUMINESCENCE OF ZINC AND MAGNESIUM COMPLEXES A. E. Kurtsevich,1 R. M. Gadirov,1 L. G. Samsonova,1 T. N. Kopylova,1 K. M. Degtyarenko,1 A. N. Gusev,2 E. V. Braga,2 and V. F. Shulgin2
UDC 535.372; 535.376; 541.65/.654; 661.783/.789
The results of spectral and luminescent study of zinc and magnesium metal complexes are presented. It is shown that radiation in mixed ligand complexes has the charge transfer character, thereby causing a low oscillator strength, large Stokes shift, and high sensitivity to the environment. These complexes are stable in the solid state, but dissociate in solutions at low concentrations. Keywords: dipyridine, ligand, metal complex, fluorescence, electroluminescence.
INTRODUCTION The luminescent organic complexes of metals find wide application in organic light-emitting diodes. The first organic light-emitting diode was created by Tang and Van Slyke [1] in 1987 based on tris(8-hydroxyquinolinoato) aluminum complex. Interest to such complexes is primarily caused by the high quantum efficiency of devices developed on their basis. Rare-earth [2, 3] and noble metal complexes [4, 5] are widespread now. Thus, the internal quantum efficiency close to 100% has been reached for iridium and platinum complexes. This is due to the fact that in metalorganic complexes of platinum group, radiation occurs from triplet states (phosphorescence), and from the spin statistics it follows that 75% of the excited molecules are formed by recombination of excitons exactly in the triplet state, and only 25% of the excited molecules are formed in the singlet state. The biggest disadvantage of the complexes based on the metals of platinum group is their highest price, because the noble metal comprises almost half of the complex mass. In an attempt to replace iridium and platinum by cheaper metals, many metal-organic complexes have been investigated. In [6, 7] high internal quantum efficiencies were obtained for a number of copper complexes due to thermally activated delayed fluorescence – the phenomenon of the increased efficiency of forming molecules emitting in singlet state that exceeds 25%, and for the best samples reaches 100%. A search for efficient emitting complexes based on inexpensive metals like beryllium, magnesium, zinc, cadmium, etc. is underway. Thus, the great attention of researchers is focused on the zinc complexes, because zinc possesses good coordinating possibilities and many its complexes exhibit intense fluorescence and electroluminescence [8–11]. At the same time, the reasons of low radiation efficiency of the metal-organic complexes are often ignored. In the present work, the spectral luminescent and electroluminescent characteristics of new metal-organic complexes (MC) based on zinc and magnesium, whose structural formulas are given below, are investigated. Quantum
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National Research Tomsk State University, Tomsk, Russia, e-mail: [email protected]; grm882
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