Luminescence of Zn2L2- and PVC-based organic molecular compositions under photo- and electroexcitation

Abstract

1 Spectral and luminescent properties of Zn2L2 complex {mu-2-bis((3-pyridine-2-il)-5-(2-salicyldeniminophenyl)- 1,2,4-triaurum(2-))dizinc(2+)solvate with ethanol} are investigated in solutions, powder, and thin polyvinylcarbazole (PVC) films. The trends in their change versus the nature, aggregate state, and excitation method are established. Electroluminescence (λmаx = 493 nm) of an ITO/PEDOT/PVC : Zn2L2/LiF/CaMg/Ag device is excited, and its current-voltage and brightness-voltage characteristics are investigated. Nowadays organic electroluminescent devices (OELD) are very popular due to numerous applications, in particular, in flat displays. They represent multilayered sandwich structures capable of converting the electric energy into light. The simplified sandwich structures comprise anode/emitting layer/cathode. Their main element is the material of the light-emitting layer. The potential material of the light-emitting layer of the electroluminescent device must have high photoluminescence intensity, thermal stability, and capability of forming thin film coatings (100 nm). From the viewpoint of further commercial production of electroluminescent devices, the material must have low cost and simple procedure of synthesis. In the last decade, the active search is on for new thin-film electroluminescent materials based on metalloorganic coordination compounds. The combination of metal ions and organic ligands in one molecule and the opportunity of purposeful change of the composition and structure of coordination compounds are favorable to the production of molecular materials for OELD with efficient electroluminescence in a wide range of wavelengths on their basis (1, 2). A special place among organic luminescent materials belonging to different classes is occupied by metal complexes with ligands comprising the C = N azomethine bond and electron-donor oxygen and/or nitrogen atoms. They are distinguished by the ease of production and thermal stability; they are capable to form thin layers and to transport electrons in them. In most cases, thin layers of organic substances of different natures are formed on the anode surface either by the vacuum deposition or centrifuging method. In the latter case, compositions including an electroactive low-molecular organic substance, an electroactive polymer, and a solvent are used. In these emitting layers, the polymeric matrix is a solid solvent for the luminophor. The processes of energy and charge transfer can proceed in the layers. At present, a search for photo- and electrostable luminophor: polymer pairs with high emissivity is urgent. However, it is difficult to develop the OELD with high efficiency and long lifetime combining the two methods of thin-film structure production (centrifuging and thermal vacuum deposition) in one device, since under laboratory conditions, it is often impossible to prevent the interaction of thin-film structures with oxygen and moisture in the