Fundamental research improves understanding of new optical materials

Fundamental research improves understanding of new optical materials

Unit cells and electron micrographs of alkaline earth chalcogenide (AeCh) nanocrystals. Credit: US Department of Energy Ames National Laboratory

Research on the synthesis of new materials could lead to more durable and environmentally friendly items such as solar panels and light-emitting diodes (LEDs). Scientists from Ames National Laboratory and Iowa State University have developed a colloidal synthesis method for alkaline earth chalcogenides. This method allows them to control the size of the nanocrystals in the material. They were also able to study the surface chemistry of the nanocrystals and assess the purity and optical properties of the materials involved. Their research is discussed in the article “Alkaline-Earth Chalcogenide Nanocrystals: Solution-Phase Synthesis, Surface Chemistry, and Stability”, published in ACS Nano.

Alkaline-earth chalcogenides are a type of semiconductor of growing interest to scientists. They have a variety of possible applications such as bioimaging, LEDs and thermal sensors. These compounds can also be used to make optical materials such as perovskites, which convert light into energy.

According to Javier Vela, Ames Laboratory Scientist and John D. Corbett Professor of Chemistry at Iowa State University, one of the reasons these new materials are exciting is that they “are composed of elements abundant in the earth and biocompatible, making them favorable alternatives to the more widely used toxic or expensive semiconductors.”

Vela explained that the most widely used semiconductors contain lead or cadmium, two elements harmful to human health and the environment. Additionally, the most popular technique used by scientists to synthesize these materials involves solid-state reactions. “These reactions often occur at extremely high temperatures (above 900°C or 1652°F) and require reaction times that can last anywhere from days to weeks,” he said.

On the other hand, Vela explained that “solution-phase (colloidal) chemistry can be achieved using much lower temperatures (below 300°C or 572°F) and shorter reaction times.” Thus, the colloidal method used by Vela’s team requires less energy and time to synthesize the materials.

Vela’s team found that the colloidal synthesis method allowed them to control the size of the nanocrystals. The size of nanocrystals is important because it determines the optical properties of certain materials. Vela explained that by changing the size of the particles, scientists can influence the ability of materials to absorb light. “This means that we can potentially synthesize materials more suitable for specific applications simply by changing the size of the nanocrystals,” he said.

According to Vela, the team’s initial goal was to synthesize semiconducting alkaline earth chalcogenide perovskites, due to their potential use in solar devices. However, to achieve this goal, they needed a deeper understanding of the basic chemistry of alkaline earth chalcogenides. Instead, they chose to focus on these binary materials.

Vela said their research fills a need to improve scientists’ understanding of photovoltaic, luminescent and thermoelectric materials that are made of earth-abundant, non-toxic elements. He said: “We hope that our developments with this project will ultimately contribute to the synthesis of more complex nanomaterials, such as alkaline earth chalcogenide perovskites.”

Study authors included Alison N. Roth, Yunhua Chen, Marquix AS Adamson, Eunbyeol Gi, Molly Wagner, Aaron J. Rossini, and Javier Vela.

Chemists use abundant, inexpensive and non-toxic elements to synthesize semiconductors

More information:
Alison N. Roth et al, Alkaline Earth Chalcogenide Nanocrystals: Solution-Phase Synthesis, Surface Chemistry, and Stability, ACS Nano (2022). DOI: 10.1021/acsnano.2c02116

Provided by Ames Laboratory

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