Indicator: Scientists make palladium light up

Organic Light Emitting Diode (OLED) displays have no competitive alternatives at present, as they offer high picture quality, fast response, low power consumption and the ability to create flexible panels. The most promising light-emitting materials for manufacturing OLED devices are considered to be organic derivatives of platinum metals. This is because such materials are theoretically capable of converting electrical charges into light with 100% efficiency. In reality, even the most promising of the currently available light-emitting materials — organic derivatives of platinum and iridium — do not meet existing technological requirements due to the high cost of the metal complexes and the rapid "burn-out" of the emitting layer. Scientists are therefore trying to improve them.

The results of the research supported by a grant from the Presidential Programme of the Russian Science Foundation are published in the journal Inorganic Chemistry.

A team of scientists from St Petersburg University (St Petersburg), the Kurnakov Institute of General and Inorganic Chemistry of the Russian Academy of Sciences (Moscow) and the University of Liverpool (UK) has developed an approach to creating a new type of light-emitting materials based on palladium compounds. The approach is unique in that the compounds were obtained from the salt of the metal and relatively simple organic molecules, with the "assembly" of a complex organic fragment being carried out directly in the coordination sphere — the closest atomic environment — of the metal. This made it possible to obtain light-emitting compounds with improved optical properties that could not be obtained by other methods. 

The researchers obtained new compounds in the form of crystals and thin polymer films. Although the individual molecules had no light-emitting properties, their crystals emitted a bright green light when irradiated with ultraviolet light. X-ray diffraction was used to determine the structure of the crystals: X-rays were passed through the crystal of the substance under investigation and reflected back to the detector along a particular path, depending on the structure of the compound under study. 

The scientists found that the distance between palladium atoms in crystals is so small that the metals interact with each other. This interaction leads to a redistribution of electrons, allowing the substance to enter a radiative state. Using calculations, the scientists found that the interaction between the palladium atoms is facilitated by a synergistic, i.e. mutually "reinforcing", combination of several types of attractive interactions between organic fragments. The scientists also showed that by replacing palladium atoms with platinum atoms, materials with yellow, orange and red emission colours can be produced. 

"Palladium belongs to the platinum group of metals and is more abundant in the Earth’s crust than platinum and iridium. However, its compounds are rarely used in light-emitting materials because of the large amount of energy dissipated as heat. We have managed not only to obtain new palladium compounds with efficient luminescence, but also, which is more importantly in my opinion, to develop a technique for designing a new type of light-emitting materials," said Mikhail Kinzhalov, Doctor of Chemistry, Associate Professor in the Department of Physical Organic Chemistry at St Petersburg University, Principal Investigator of the project supported by a grant from the Russian Science Foundation.