Advanced “superplank” material shows LED-like light when heated

Advanced Super-Planckian material exhibits LED-like light when heated. Credit: Rensselaer Polytechnic Institute

Could there be a new kind of light in the universe? From the end of the 19th century, scientists realized that when heated, all materials emit light with a predictable wavelength spectrum. Study published today in Nature Scientific reports represents a material that emits light when heated, which goes beyond the limits established by this natural law.

In 1900, Max Planck first mathematically described the radiation pattern and opened the quantum era, suggesting that energy can exist only in discrete values. Just like poker on a fireplace glows red materials emit more intense radiation, and the peak of the emitted spectrum shifts toward longer waves with increasing temperature. According to Planck’s law, nothing can emit more radiation than a hypothetical object that perfectly absorbs energy, the so-called “black body”.

New material discovered by Sean Yu Lin, lead author and professor of physics at the Rensselaer Polytechnic, challenges the limitations of Planck's law by emitting a consistent light coloured similar to what is produced by lasers or LEDs, but without the expensive structure needed to produce stimulated radiation from these technologies. In addition to the study of spectroscopy just published in Nature Scientific reportsLin previously published an image study in IEEE Photonics JournalBoth show a burst of radiation of about 1.7 microns, which is the near infrared part of the electromagnetic spectrum.

“These two articles are the most convincing evidence of“ superplank ”radiation in the far zone,” Lin said. “This does not violate Planck’s law. This is a new way of generating thermal radiation, a new basic principle. This material and the method that he represents opens up a new path for creating ultra-intense customizable LED infrared emitters for thermovoltaics and the efficient use of energy. "

For his research, Lin built a three-dimensional tungsten photonic crystal – a material that can control the properties of a photon – with six layers displaced, in a configuration similar to a diamond crystal, and coated on top optical cavity it clears the light even more. A photonic crystal compresses the spectrum of light emitted by a material to a range of about 1 micrometer. The cavity continues to compress energy in the range of about 0.07 micrometers.

Lin has been working to create this progress for 17 years since he created the first all-metal photonic crystal in 2002, and these two works represent the most rigorous tests he conducted.

“Experimentally, this is very solid, and as an experimenter, I support my data. From a theoretical point of view, no one has a theory that could fully explain my discovery, ”Lin said.

In both image research and spectroscopy, Lin prepared his own sample and black body control element – coating vertically aligned nanotubes on top of the material – next to one piece of silicon substrate, eliminating the possibility of changes between sample testing and control, which could jeopardize the results. In the experimental vacuum chamber, the sample and control were heated to 600 degrees Kelvin, about 620 degrees Fahrenheit.

IN Nature Scientific reportsLin presents a spectral analysis taken in five positions when the aperture of an infrared spectrometer moves from a view filled with a black body to one of the materials. Peak radiation with an intensity of 8 times the black body standard is 1.7 micrometers.

IEEE Photonics Journal The document presents images obtained using a conventional device with a charge-coupled close to infrared camera that can capture the expected radiation of the material.

Recent unrelated studies have shown a similar effect at a distance of less than 2 heat waves from the sample, but Lins is the first material to display super-Planck radiation when measured from a distance of 30 centimeters (about 200,000 wavelengths), causing the light to completely escape from the surface of the material .

Although theory does not fully explain the effect, Lin hypothesizes that displacements between layers photonic crystal allow light to appear from within many spaces within the crystal. The emitted light is reflected back and forth within the crystalline structure, which changes the property of light as it moves to the surface to meet an optical resonator.

“We think that light comes from inside the crystal, but there are so many planes in the structure, so many surfaces that act like oscillators, so much excitation that it behaves almost like an artificial laser material,” Lin said. “It's just not an ordinary surface.”

The new material can be used in areas such as energy collection, tracking and identification of objects based on military infrared radiation, the creation of highly efficient optical sources in the infrared range controlled by waste heat or local heaters, studies requiring ecological and atmospheric and chemical spectroscopy in the infrared range, and in optical physics as a laser-like heat emitter.

Crystal creates a breakthrough in the supercontinuum

Additional Information:
“In-situ and direct confirmation of superplank thermal radiation emitted by a metallic photonic crystal at an optical wavelength” Scientific reports (2020).

Advanced “superplank” material exhibits light similar to an LED when heated (2020, March 23)
restored March 23, 2020

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