New colloidal synthesis method for alkaline earth chalcogenides

Research into the synthesis of new materials could lead to more sustainable 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. The researchers were also able to study the surface chemistry of the nanocrystals and assess the purity and optical properties of the materials involved.

Alkaline earth chalcogenides are a type of semiconductor with a variety of possible applications such as bioimaging, LEDs, and thermal sensors. These compounds may also be used to make optical materials such as perovskites, which convert light into energy. Javier Vela, Ames Lab scientist and the John D. Corbett Professor of Chemistry at Iowa State University, said these new materials are of interest because they are composed of earth-abundant and biocompatible elements, which make them favourable alternatives compared to the more widely used toxic or expensive semiconductors.

Vela said that the more widely used semiconductors contain lead or cadmium, which can be detrimental to human health and the environment. Additionally, a common technique used by scientists to synthesise 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,” Vela said.

On the other hand, solution-phase (colloidal) chemistry can be performed using much lower (below 300°C or 572°F) temperatures and shorter reaction times. Therefore, the colloidal method used by Vela’s team of researchers requires less energy and time to synthesise the materials. The researchers found that the colloidal synthesis method allowed them to control the size of the nanocrystals; nanocrystal size is important because it determines the optical properties of some materials. Vela said that by changing the size of the particles, scientists can influence how well the materials absorb light. “This means we can potentially synthesise materials that are more suited for specific applications just by changing the nanocrystal size.”

According to Vela, the team’s original goal was to synthesise semiconducting alkaline earth chalcogenide perovskites, because of their potential use in solar devices. However, to accomplish this goal, the researchers needed a deeper understanding of the fundamental chemistry of alkaline earth chalcogenides. As a result, they chose to focus on these binary materials instead. Vela said the research fills a need to improve scientists’ understanding of photovoltaic, luminescent and thermoelectric materials that are made of earth-abundant and non-toxic elements. “We hope that our developments with this project ultimately aid in the synthesis of more complex nanomaterials, such as the alkaline earth chalcogenide perovskites,” Vela said.

The research is further discussed in a paper published in ACS Nano.

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