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Ontario Technoblog

Ontario Emperor technology blog.

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Wednesday, January 04, 2006

Revisiting White Light Generator

At starshipbuilder.com, thomas7g has not only linked to my October post regarding Michael Bowers' research that resulted in white light-emitting quantum dots, but has also linked to a National Geographic article on the topic. Here's an excerpt:

The lightbulbs in your home are still very similar to the ones first invented by Thomas Edison over a century ago.

An incandescent bulb is a glass tube filled with a non-reactive gas that contains a thin metal filament. When electric current runs through the filament, the atoms within the filament vibrate, causing it to emit both light and lots of heat.

The heat is wasted energy. Researchers have long anticipated that LEDs, found in everything from digital clocks to car dashboards, could replace lightbulbs.

LEDs use a greater proportion of the electricity flowing through them, so they emit less heat. In fact, LEDs are cool to the touch.

This translates into savings for consumers. Widespread adoption of LEDs could cut U.S. consumption of electricity for lighting by 29 percent, according to the U.S. Department of Energy.

And unlike fragile glass bulbs, LEDS are made from sturdy wafers of semiconducting materials. An LED can last up to 50,000 hours—50 times as long as a 60-watt bulb.

But creating white-light LEDs has been problematic....


However, only The Spoof reports what happened (?) next:

Having "accidentally" discovered the light bulb of the future on his first try, Vanderbilt graduate student Michael Bowers tried an additional 1300 ways to construct his breakthrough "bulb" which consists of a blue LED coated with "microdots." "My engineering advisor always quoted Edison's statement that "Invention was 1% inspiration, and 99% perspiration. I happened to get the inspiration part first, I guess."

To avoid "shortchanging" engineers world-wide, and making a fool out of Edison, who really should have given up after a couple hundred failures, Bowers was forced by Vanderbilt professors to try making his microdots bigger, smaller, coating them on regular light bulbs, halogen headlights, Maglites, even fireflies, which he dipped into epoxy and rolled around in the dots....


Truth to tell, Bowers wasn't working in a vacuum (that's another scientific endeavor). Here's what Lawrence Livermore National Laboratory was saying in 2000:

Physicist Howard Lee and his team of Laboratory and University of California at Davis researchers have been exploring [quantum dots], which are about a single nanometer (a billionth of a meter) in size and made out of material such as silicon. Lee explains, "Imagine taking a wafer of silicon and cutting it in half again and again and again, until you have a piece containing about a hundred to a thousand atoms. That's the size we're looking at."

The small size results in new quantum phenomena that yield some extraordinary bonuses. Material properties change dramatically because quantum effects arise from the confinement of electrons and "holes" in the material (a hole is the absence of an electron; the hole behaves as though it were a positively charged particle). Size changes other material properties such as the electrical and nonlinear optical properties of a material, making them very different from those of the material's bulk form. If a dot is excited, the smaller the dot, the higher the energy and intensity of its emitted light. Hence, these very small, semiconducting quantum dots are gateways to an enormous array of possible applications and new technologies....

Another future use for quantum-dot LEDs is to emit white light for uses in laptop computers or as internal lighting for buildings or cars. Lee and his team have discovered they can-by controlling the amount of blue in the emission-control the "flavor" or "tone" of the white light as well....


And here's what Sandia National Laboratories said in 2003:

In a different approach to creating white light several researchers at the Department of Energy’s (DOE) Sandia National Laboratories have developed the first solid-state white light-emitting device using quantum dots. In the future, the use of quantum dots as light-emitting phosphors may represent a major application of nanotechnology.

“Understanding the physics of luminescence at the nanoscale and applying this knowledge to develop quantum dot-based light sources is the focus of this work,” says Lauren Rohwer, principal investigator. “Highly efficient, low-cost quantum dot-based lighting would represent a revolution in lighting technology through nanoscience.”

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