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Three teams of Clemson University researchers have teamed up to discover some of the mysteries surrounding perovskite nanocrystals, which are semiconductors with various applications, including LEDs, lasers, solar cells and photodetectors.

A research article entitled ‘The Correlation Between Phase Transition and Photoluminescence Properties of CsPbX₃ (X = Cl, Br, I) perovskite nanocrystals “recently appeared in Nanoscale Advances, an open-access journal published by the Royal Society of Chemistry. The lead author of the article is Jun Yi, who was a student who worked with Apparao Rao, the Robert Adger Bowen professor of physics at Clemson University.

“We are always looking for students to work on projects,” said Rao, a professor in the Department of Physics and Astronomy at the College of Science and director of the Clemson Nanomaterials Institute. “Jun started this project about a year ago, and our teams worked together and came up with a nice piece of work. In fact, the magazine presented our work on the back cover.”

Rao said Yi could be divided between Rao’s team and a team led by Jianbo Gao, assistant professor of physics and astronomy; and a third team, led by Hugo Sanabria, an associate professor of physics and astronomy.

Rao and Gao explained that their common interests in the small nanocrystals are focused on the optical properties and applications of the material.

“The Jianbo team and my team have a common interest in advancing nanocrystals to produce better solar cells, LEDs – things like that,” Rao said. “In principle, the three teams had the necessary tools to complete the study.” The study has relevance to applications that have found their way into our lives, according to Gao.

“This technology is widely used. You can find it at Costco or Walmart, for example, because it is present in the quantum dots that Samsung uses in its QLED TV,” Gao said.

The authors noted in the paper that perovskite nanocrystal “attracts a lot of attention because of its unique tunable optical properties.”

With these special nanocrystals, the teams’ research deals with a phase transition, one of the most fundamental physical phenomena in natural physics, which can affect the electrical, optical, magnetic, mechanical and chemical properties of materials. Using nanocrystals made, in part, of sugar, bromine or iodine, the researchers discovered that when exposed to heat, the chlorine-based nanocrystals behaved differently from the iodide- or bromine-based nanocrystals.

“That got us thinking about what the reason might be,” Rao said.

The paper concluded that the teams’ research “provides a deeper insight into the impact of phase transition on the low-temperature photo-physics of perovskite materials.”

“We laid the groundwork and connected the dots,” Gao said.

Ironically, the paper was not ready until Yi returned to his home in China.

“We were stumped for a while,” Gao said.

“Without this student, we could not have achieved this research project. He increased the level of the paper,” Rao added.