My watch list
my.chemeurope.com  
Login  

Harnessing the rattling motion of oxygen ions to convert T-rays to visible light

01-Dec-2017

ACS Nano

Top: A schematic representation of the nanoscale cages. The oxygen anions randomly occupy one sixth of the cages. Bottom: A photograph of the emission of visible light at a terahertz radiation level of 0.21 and output power of 50 W

Scientists have successfully visualized terahertz radiation, popularly known as T-rays, using a crystal called mayenite (Ca12Al14O33). Their method cleverly utilizes the rattling motion caused by the vibration of oxygen ions inside the cage-like structures of the crystal.

In recent years, there has been growing interest in developing practical devices based on terahertz technology. With wavelengths longer than infrared light, T-rays are considered safer than conventional imaging systems. They are already used, for example, at airport security checkpoints, and are starting to be used more widely in areas such as medical screening, food inspection and analysis of artworks. The visualization of terahertz light itself, however, has so far proved challenging.

Now, Hideo Hosono of Materials Research Center for Element Strategy, Tokyo Tech and co-workers in Japan, Ukraine and the US have devised a simple approach to convert T-rays to bright, visible light.

First, the study involved beaming T-rays onto the mayenite crystal using a gyrotron. This led to the vibration of oxygen anions, which collide with the inside walls of the cages within the crystal. Each cage has an inner diameter of 0.4 nanometers and an outer diameter of 0.7 nanometers.

"The rattling of oxygen ions within the cages promotes upward energy conversion," Hosono explains. "Strong and frequent collisions of the oxygen ions induce electron transfer to neighboring empty cages. The excitation of the oxygen ions is key to the emission of visible light."

Spectroscopy measurements confirmed that the visible light originated from vibrations caused by the free-moving oxygen anions. The researchers took care to rule out the possibility of other sources such as black body radiation and surface polarization as reasons behind the production of visible light.

The study is an example of strategic research on functional materials under the Element Strategy initiative supported by Japan's Ministry of Education, Culture, Sports, Science and Technology (MEXT) and the Japan Science and Technology Agency (JST).

"The crystal in our study is just composed of calcium, aluminium and oxygen, all of which are in the top five of the most abundant elements," says Hosono. "So, it's one of the most inexpensive materials, at around 15 cents per kilogram."

Despite its simplicity, Hosono says that the crystal has many exciting properties due to its nanostructure. Drawing on 20 years of research, his group has already succeeded in demonstrating that the material has excellent catalytic properties for ammonia synthesis and superconductivity.

Best known for his pioneering work on iron-based superconductors, Hosono says that the current study marks a new research direction. "Our group has been concentrating on the cultivation of new functionalities using abundant elements, but it's the first time for me to focus on ionic motion -- this is completely new," he says.

The findings could lead to the development of a T-ray detector, as no such conventional detector has yet been designed.

Hosono adds: "Right now, our material is good at detecting strong terahertz radiation. The challenge will be how to adjust the sensitivity."

His group has also reported that the oxygen anions can be substituted with gold or hydrogen anions inside the cages. By making use of these different anions, it may be possible to develop detectors that emit different-colored light in future.

Facts, background information, dossiers
  • imaging systems
  • functional materials
  • electron transfer
  • polarization
  • mayenite
More about Tokyo Institute of Technology
  • News

    Oxidation of sulfides with perovskite catalyst

    Researchers at Tokyo Institute of Technology have developed a ruthenium-based perovskite catalyst that shows strong activity even at low temperatures (down to 313 K). The reusable catalyst does not require additives, meaning that it can prevent the formation of toxic by-products. The oxidat ... more

    Reducing CO2 with common elements and sunlight

    An international collaborative research group including Tokyo Institute of Technology, Universite PARIS DIDEROT, and CNRS has discovered that CO2 is selectively reduced to CO when a photocatalyst composed of an organic semiconductor material and an iron complex is exposed to visible light. ... more

    Anthracenes orbiting fullerenes

    Saturn is the second largest planet in our solar system and has a characteristic ring. Japanese researchers have now synthesized a molecular “nano-Saturn”. As the scientists report, it consists of a spherical C60 fullerene as the planet and a flat macrocycle made of six anthracene units as ... more

Your browser is not current. Microsoft Internet Explorer 6.0 does not support some functions on Chemie.DE