High-entropy compounds, which consist of five or more elements in equal proportions, can be used to create emitting elements, batteries, catalysts and thermal barrier coatings. For instance, materials containing oxides of rare earth metals (yttrium, europium, gadolinium, lanthanum and erbium) can glow in the green and red ranges, which makes them a good basis for light-emitting diodes and light converters. Their structure provides high stability, as the combination of different atoms hinders the formation of defects that can reduce the efficiency of the material.
However, it remained unclear until recently in what way the optical properties of the materials depend on the structure of the compound, the conditions of its synthesis and the presence of impurities. To answer this question, the scientists from Yekaterinburg synthesized a high-entropy oxide containing atoms of yttrium, gadolinium, lanthanum and erbium with the help of the co-precipitation method. This method is a chemical process in which hydroxides of the desired metals are precipitated from solutions. In order to obtain the oxide, this precipitate was heated at a temperature of 200 to 800 degrees Celsius for two hours.
The experiment showed that the optimal synthesis temperature is 680 degrees Celsius. Under these conditions, the nanopowders transitioned from an amorphous state (with randomly arranged atoms) to a crystalline state (with a constant structure and an ordered atomic lattice). This structure ensured a uniform distribution of ions, improving the optical properties of the nanopowders. The transition also caused the band gap to widen, making the material more transparent. Finally, as a result of the temperature increase, glow intensity grew more than fourfold.
The scientists believe that the synthesized materials will facilitate the creation of new types of optoelectronic devices capable of operating in extreme conditions. These include LEDs, which will retain their brightness when heated without fading over time.
“The newly-developed material can be used in next-generation LEDs with improved brightness and durability, in ultraviolet emitters for medical and industrial applications, and in biomedical devices such as sensors and diagnostic equipment. In the future, we plan to adapt its properties to create devices operating in the infrared and visible ranges so as to expand its potential application,” Evgeny Buntov, candidate of physical and mathematical sciences, is quoted as saying by the Russian Science Foundation.
