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Prototype cathode-ray bulb can compete with LEDs, say Russian researchers

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A prototype cathodoluminescent lamp has been developed by Russian researchers, who say it is more reliable, durable and luminous than any of its equivalents worldwide.

A team from the Moscow Institute of Physics and Technology (MIPT) and Lebedev Physical Institute of the Russian Academy of Sciences developed the new lamp, which relies on the phenomenon of field emissions to emit light.

While LED lamps have become commonplace, they are not the only clean and power-saving alternative to incandescent lamps.

The new bulbs rely on the same principle that powered old TVs using cathode-ray tubes. A negatively charged electrode, or cathode, at one end of a vacuum tube serves as an electron gun.

A potential difference of up to 10 kilovolts accelerates the emitted electrons toward a flat positively charged phosphor-coated electrode - the anode - at the opposite end of the tube. This electron bombardment results in light.

Cathodoluminescent lamps have the advantage of being able to emit light almost at any wavelength, from the red to ultraviolet, depending on which fluorescent material is used.

The researchers say their bulb can replace ultraviolet fluorescent tubes, often used in greenhouses, which have been affected by the Minamata Convention, a United Nations treaty signed by 128 countries that bans mercury in household products.

Cathodoluminescent UV light bulbs contain no mercury and are generally cleaner in service and upon disposal.

“Some industries using mercury lamps for water treatment and air disinfection, for example, will be very slow and unwilling to phase them out,” said Mikhail Danilkin of Lebedev Physical Institute.

“Medicine is different, because the issue of mercury lamp disposal at individual medical facilities has not been resolved, while the environmental standards are becoming stricter. Cathodoluminescent lamps could be used in operating room decontamination, UV irradiation of throat and tonsils, and dental filling curing.”

Another important advantage of the new lamp over LEDs and fluorescent bulbs is that it does not rely on the so-called critical raw materials. These include gallium, indium and some rare-earth elements.

While their supply is limited, these materials are essential and irreplaceable in the health, defense, aerospace and other key industries.

Attempts to mass-produce commercial cathodoluminescent light bulbs have been made in the United States, but the consumers did not embrace the device, mostly because it was bulky and took several seconds to warm up the cathode to operating temperature.

Some cathodes, known as field emission cathodes, do not require any warm-up, but designing an efficient, long-lasting and technologically advanced cathode that could be mass-produced and sold at an affordable price has proved challenging.

Despite ongoing efforts in Japan and the US, the Russian team says its study marks the first successful attempt at this.

“Our field emission cathode is made of ordinary carbon,” said Professor Evgenii Sheshin, deputy chair of vacuum electronics at MIPT, who led the research team. “This carbon is not used merely as a chemical, but rather as a structure. We found a way to fashion a structure from carbon fibres that is resistant to ion bombardment, outputs a high-emission current, is technological and affordable in production. This technology is our know-how, no one else in the world has it.”

By subjecting the carbon to special treatment, many sub-micrometer protrusions - less than a millionth of a metre in size - are formed at the tip of the cathode. This results in an ultra-high electric field at the tip, driving electrons out, into the vacuum.

The MIPT research group has also developed a compact power source for their cathodoluminescent lamp, which supplies enough kilovolts for successful field electron emission. The source is fitted around the glass light bulb with almost no effect on its size.

The team believes that, if mass-produced, the new cathodoluminescent bulb could compete with the cheap lamps based on light-emitting diodes. The new bulb would also help phase out the hazardous fluorescent lamps containing mercury, which are still used in many households.

“Unlike the LED bulb, our lamp is not afraid of elevated temperatures. You can use it where diodes quickly fade, such as in ceiling spotlights, where insufficient cooling is provided,” added study co-author Dmitry Ozol from MIPT’s vacuum electronics department.

In 2018, the EU instituted a ban on the sale of halogen bulbs in an effort to increase the efficiency of lighting on the continent.

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