Riken scientists have shown how carbon nanoral tubes can absorb light and the formation of dark excitons through phonon interactions and the formation of dark excitons. This could pave the way for breakthroughs in solar energy and futuristic photonic devices.
Three physicists from the Japanese Riken Center for Advanced photonics have uncovered how ultra -thin carbon tubes, which are referred to as carbon nanor tubes, can emit light that bears more energy than the light that you absorb. This surprising discovery could pave the way for new technologies in the solar energy harvest and the advanced biological imaging.
Most of us are familiar with the lights of some materials under ultraviolet light (UV) such as fluorescent colors. These are classic examples of photoluminescence, in which a material absorbs a high energy-UV light and then releases the visible light with low energy.
The strange case of upward conversion
But the opposite can happen in some materials. Light them on them with low energy and in return they emit higher energies light. This rare and contraguitive process is referred to as the structure-photoluminescence (UCPL). It is of growing interest because it could improve solar cell efficiency by converting unusable light into electrically producing energetic light with low energy.
In typical photoluminescence, incoming light excites an electron that lifts it to a higher energy level and leaves a positive “hole”. The electron and the hole briefly form a bound state that is referred to as exciton. Finally, they recombinate and release light.
Phonon interactions lower Ucpl
With normal photoluminescence, the Exziton loses energy to the material, and therefore the emitted light carries less energy than the incoming light. In UCPL, however, the Exziton receives an energy push from the material by interact with vibrations called phonons from the material.
Now Yuichiro Kato and two colleagues, all in the Riken Center for Advanced Photonics, have determined exactly how UCPL works in a single-walled carbon nanor tubes-and the drinking strap-like cylinders of carbon, only a few billion height of meters wide.
Earlier theories had proposed that UCPL could only occur in well -being carbon nanor tubes if excitons were temporarily caught by defects in the structure of the nanor tube. However, the researchers found that UCPL occurred with high efficiency even with infallible nanor tubes, which indicates that an alternative mechanism worked.
Dark excitons: secret for higher energy emissions
The trio found that an electron, if it is enthusiastic about light, receives a simultaneous energy push from a phonon to form a “dark Exziton” state. After the Exziton has lost a little energy, it finally spends light with more energy than the incoming laser.
The increase in the temperature led to a stronger UCPL effect and confirmed the predictions of its model. “Phonons are more common at higher temperatures and improve the likelihood of phonon-mediated transitions,” says Kato.
Future possibilities for energy and cooling
The researchers plan to examine the opportunity to cool a nanor tube using laser lighting in order to remove the thermal energy by UCPL and to examine energy services for creating a device on a nanor tube base.
“By determining an intrinsic model from UCPL in a single -walled carbon nanoral tubes, we hope to open up new opportunities for the design of advanced optoelectronic and photonic devices,” says Kato.
Reference: “Intrinsic process for the increase in photoluminescence over -moment -Phonon -Phonon coupling in carbon nanorale tubes” by Daichi Kozawa, Shun Fujii and Yuichiro K. Kato, October 10, 2024, Physical evaluation B.
DOI: 10.1103/Physrevb.110.155418
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