Science

Nanoparticle tech could make for brighter, longer-lasting LEDs

Nanoparticle tech could make f...
An array of conventional LED diodes, as used within an LED light bulb
An array of conventional LED diodes, as used within an LED light bulb
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An array of conventional LED diodes, as used within an LED light bulb
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An array of conventional LED diodes, as used within an LED light bulb
A diagram depicting the nanoparticle layer (blue dots) above the LED chip (yellow)
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A diagram depicting the nanoparticle layer (blue dots) above the LED chip (yellow)

As compared to their incandescent counterparts, LED bulbs are already known for producing a lot of light using relatively little electricity. According to a new study, however, a thin layer of nanoparticles could allow them to perform even better.

A typical LED diode consists of the actual light-emitting LED chip, which is surrounded by a transparent protective domed casing/lens. And while much of the light produced by the chip passes right through the casing, some of it is reflected back inwards.

Unfortunately that reflected light is wasted, as it doesn't travel out into the diode's surroundings to provide illumination. Additionally, it raises the temperature inside the diode, causing the chip to degrade faster – this means that the LED ultimately won't last as long as it would otherwise.

Seeking a solution to the problem, scientists at Imperial College London and the Indian Institute of Technology Guwahati recently developed a computer model in which a transparent layer of inexpensive metallic nanoparticles was added above the LED chip, between it and the inside of the casing.

A diagram depicting the nanoparticle layer (blue dots) above the LED chip (yellow)
A diagram depicting the nanoparticle layer (blue dots) above the LED chip (yellow)

The particles acted somewhat like a grid of micro-lenses, altering the angle at which the light met the casing material. As a result, up to 20 percent more light was able to pass through, as opposed to being reflected back in. This means that a greater amount of light could be emitted using the same amount of electricity, plus the LEDs should stay cooler and thus have a longer lifetime.

Plans now call for the production of prototype diodes utilizing the technology, so that variables such as nanoparticle material, size, shape and spacing can be tested and tweaked.

"While improvements to the casing have been suggested previously, most make the LED bulkier or more difficult to manufacture, diminishing the economic effect of the improvement," says IIT Guwahati's Dr. Debabrata Sikdar, co-author of a paper on the research. "We think that our innovation, based on fundamental theory and the detailed, balanced optimization analysis we performed, could be introduced into existing manufacturing processes with little disruption or added bulk."

The paper was published in the journal Light: Science & Applications.

Source: Imperial College London

7 comments
wolf0579
OK... so, LED's are photovoltaic cells in reverse. This must have some impact on the PV industry. I wonder if any of the PV companies have heard about this?
christopher
So desperately needed - I *hate* it when my LEDs wear out!!
Sean Reynolds
The LED is not the issue though... the lightbulb manufacturers put cheep power electronics in their bulbs so they flicker or go out before they should.
Karmudjun
You know Ben, I've looked at LEDs and heard that 100 lumens per watt was the ideal minimum efficiency of quality LED bulbs. For my dwelling, I've been hard pressed to find any that meet that standard. Maybe with this improvement of ~20% more light from the same electronics will meet or exceed this theoretical minimum efficiency. I'd sure like to see that!

Good article, thanks!
McDesign
This is my field - the leadoff picture is a type of lamp (multiple white 5mm LEDs) not used in a decade, except in cheap consumer catalogs.

ALL illumination LEDs use a 450 nanometer chip - the royal blue color of police lights (a vanishingly small proportion use a 405 nm "violet" pump).

All of these LEDs are covered with a phosphor coating that absorbs a proportion of this blue light and re-radiates it at various longer (towards red) wavelengths. Our eye mixes all this into "white" light - obviously of varied quality!

The Commercial/Industrial fixtures I work on at the moment have a "wall-plug efficacy" of the entire luminaire of 150-180 lumens per Watt.

Anyway - not clear to me where these nanoparticles go in the LED sandwich - between the chip and phosphor?
ljaques
20% is a decent increase in light output. What is the decrease in lifetime? Most LEDs are 30k, 50k, or 100k hour MTBF. Depending on how costly this turns out to implement, it should be a great boon to smaller lights on mobile units, etc. Hope to see it developed! We need to pare our total electrical use, moving to efficient nanowatt tech when it's developed. (Wolf, WTH? PV wasn't mentioned in the article.)
McDesign
In lighting, the rule of thumb is that without a constant reference, it takes ~30% brightness change to be noticeable.