Fibrous red phosphorous all aglow when confining electrons

When electrons are confined into very small spaces, they can exhibit unusual electrical, optical and magnetic behavior. From confining electrons in two-dimensional atomic sheet graphene to restricting electrons even further to achieve one-dimensionality, this broad line of research is transforming the landscape of fundamental research and technological advances in physics, chemistry, energy harvesting, information and beyond.

Now, in a paper in Nature Communications, an international team led by researchers at Aalto University in Finland reports that confining electrons in the one-dimensional sub-units of fibrous red phosphorous can cause this material to show large optical responses – that is, it shows strong photoluminescence under light irradiation.

Red phosphorous, like graphene, belongs to a unique group of materials called one-dimensional van der Waals (1D vdW) materials. A 1D vdW material is a radically new type of material that was only discovered in 2017. Until now, research on 1vdW materials has focused on their electrical properties.

The team uncovered the optical properties of 1D vdW fibrous red phosphorous by conducting measurements with techniques like photoluminescence spectroscopy, where they shone laser light on the samples and measured the color and brightness of the light emitted back. Their findings show that the 1D vdW material demonstrates giant anisotropic linear and non-linear optical responses – in other words, the optical responses strongly depend on the orientation of the fibrous phosphorous crystal. As does the emission intensity, which relates to the number of photons emitted during a specific time.

"The way it responded in the experiments makes 1D vdW fibrous red phosphorus a really exciting material," says Luojun Du, a postdoctoral researcher at Aalto University. "For example, it shows both giant anisotropic linear and non-linear responses as well as emission intensity, which is striking."

The material’s photoluminescence – the effect commonly seen in everyday life in reflective signs or children’s glow-in-the-dark toys when light is emitted after absorption – also struck the researchers by surprise. The team compared the photoluminescence of fibrous red phosphorous with monolayer molybdenum disulfide (MoS₂), which is well-known for strong photoluminescence, and found that its photoluminescence was more than 40 times more intense, making it ultra-bright – albeit very briefly.

"The strong photoluminescence of fibrous red phosphorus is unexpected," says Du. "In fact, we initially expected that the photoluminescence of fibrous red phosphorous would be only weak. Based on theoretical calculations, this effect shouldn’t actually be strong so we’re now doing more experiments to clarify the origin of its after-glow."

"I believe that one-dimensional van der Waals materials like fibrous red phosphorous show real promise for displays and other applications which rely on materials that demonstrate exactly the behaviors we’ve seen in this study," says Zhipei Sun, a professor at Aalto University who leads the group behind the study. "The spectrum of its anisotropic optical response also seems to be very wide if we compare it with responses from conventional materials."

This story is adapted from material from Aalto University, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.