One-dimensional fibrous red phosphorus shines unexpectedly

The researchers used the exceptional facilities of Micronova Nanofabrication Cleanroom. Credit: Mikko Raskinen / Aalto University

New study published in Nature Communication is the first to show strong optical properties in a 1D van der Waal material.

When electrons are confined in very small spaces, they can exhibit unusual electrical, optical and magnetic behavior. On the confinement of electrons in a two-dimensional atomic sheet graphene – a feat that won the Nobel Prize for Physics in 2010 – to further restrict electrons to achieve unidimensionality, this vast line of research transforms the landscape of basic research and technological advances in physics, chemistry, recovery of energy, information and beyond.

In a study published in Nature Communication, an international team led by researchers at Aalto University has now found that fibrous red phosphorus, when electrons are confined to its one-dimensional subunits, can exhibit large optical responses, that is, the material exhibits strong photoluminescence under light irradiation. Red phosphorus, 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 electrical properties.

The team discovered the optical properties of 1D vdW fibrous red phosphor through measurements such as photoluminescence spectroscopy, where they shed laser light on the samples and measured the color and brightness of the light returned. The results show that the vdW 1D material exhibits giant anisotropic linear and nonlinear optical responses – in other words, the optical responses strongly depend on the orientation of the fibrous phosphorus crystal – as well as on the emission intensity, which is related 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. For example, it shows both linear and non-linear giant anisotropic responses as well as the intensity of the emissions, which is striking, ”says Dr Luojun Du, postdoctoral researcher at Aalto University.

The material’s photoluminescence – the effect commonly seen in everyday life in reflective panels or children’s phosphorescent toys, when light is emitted after absorption – also surprised the researchers. The team compared the photoluminescence of fibrous red phosphorus with monolayer molybdenum disulfide (MoS2), which is well known for its strong photoluminescence, and found that the intensity of the photoluminescence was more than 40 times stronger, which Makes it ultra-bright – albeit very briefly.

“The strong photoluminescence of fibrous red phosphorus is unexpected. Indeed, it was initially expected that the photoluminescence of the fibrous red phosphorus was only weak. Based on theoretical calculations, this effect should not be really strong, so we are now doing more experiments to clarify the origin of its afterglow, ”says Du.

“I think one-dimensional van der Waals materials like fibrous red phosphorus show real promise for displays and other applications, which rely on materials that demonstrate exactly the behaviors we observed in this study. The spectrum of its anisotropic optical response also appears to be very broad when compared to the responses of conventional materials, ”said Professor Zhipei Sun, who heads the group behind the study.

Reference: “Giant Anisotropic Photonics in Fibrous Red Phosphorus Semiconductor 1D van der Waals” by Luojun Du, Yanchong Zhao, Linlu Wu, Xuerong Hu, Lide Yao, Yadong Wang, Xueyin Bai, Yunyun Dai, Jingsi Qiao, Md Gius Uddin , Xiaomei Li, Jouko Lahtinen, Xuedong Bai, Guangyu Zhang, Wei Ji and Zhipei Sun, August 10, 2021, Nature Communication.
DOI: 10.1038 / s41467-021-25104-6

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