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Carbon Nanotube-Based Lights More Efficient than LEDs

Photonics.com
Oct 2014
SENDAI, Japan, Oct. 15, 2014 — A new carbon nanotube-based light source touts power consumption that is about a hundred times lower than that of an LED.

A team from Tohoku University developed the new light source, which uses around 0.1 W for every hour of operation. Carbon nanotubes (CNTs) are poised to replace silicon in making semiconductor materials, they said, and have the potential to meet the ever-increasing demand for greener bulbs and lighting devices.

The new device is based on a phosphor screen and single-walled CNTs as electrodes in a diode structure. Specifically, the new device was assembled from a mixture liquid containing highly crystalline single-walled CNTs dispersed in an organic solvent that was mixed with a surfactant.

The researchers painted the mixture onto the positive electrode or cathode, and scratched the surface with sandpaper to form a light panel capable of producing a large, stable and homogenous emission current with low energy consumption.

“Our simple diode panel could obtain high brightness efficiency of 60 lumen per watt, which holds excellent potential for a lighting device with low power consumption,” said Norihiro Shimoi, associate professor of environmental studies at Tohoku, noting that while the device has a diode-like structure, its light-emitting system is not based on a diode system.

The device features a luminescence system that functions more like cathode ray tubes, with CNTs acting as cathodes and a phosphor screen in a vacuum cavity acting as the anode. Under a strong electric field, the cathode emits tight, high-speed beams of electrons through its sharp nanotube tips (a process known as field emission). The electrons then fly through the vacuum in the cavity and hit the phosphor screen, prompting it to glow.

Field emission electron sources require much less power to operate and produce a much more directional and easily controllable stream of electrons. They have the ability to provide intense electron beams that are about a thousand times denser than conventional thermionic cathodes, according to the researchers.

“We have found that a cathode with highly crystalline single-walled carbon nanotubes and an anode with the improved phosphor screen in our diode structure obtained no flicker field emission current and good brightness homogeneity,” Shimoi said.

The research was published in Review of Scientific Instruments (doi: 10.1063/1.4895913).

For more information, visit www.tohoku.ac.jp.


GLOSSARY
cathode
1. The negative electrode of a device in an electrical circuit. 2. The positive electrode of a primary cell or storage battery. 3. The primary source of electrons in an electron tube, serving as the filament in a directly heated electron tube, and in a coated metal configuration surrounding the heater in an indirectly heated one.
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