a new way to make solid-state lights that produce white light.

Inside the Vanderbilt chemistry building last spring, McBride and Bowers were experimenting with quantum dots — tiny semiconductor crystals of cadmium selenide that absorb light and generate a charge.

McBride, who was studying the way quantum dots grow, had asked Bowers repeatedly to make batches of smaller and smaller crystals. Bowers, a graduate student in chemistry, put the nanocrystals into a small glass cell and illuminated it with a laser, expecting to see blue light.

Instead he saw white.

The surprise discovery was that the tiny crystals can absorb blue light produced by light-emitting diodes, or LEDs, and emit a warm white light.

Bowers then borrowed polyurethane from another student and coated a small LED. The result was proof that quantum dots, if made small enough, could be used to make a white light source.

Read the article : http://www.ashlandcitytimes.com/apps/pbcs.dll/article?AID=/20061206/NEWS0201/612060431/1291/MTCN01

maybe in a few years I will understand all of that. For now, all i can say is cool

thanks for the link

what is "solid state"?

Originally 'solid state' ment non-tube/relay/dohickey based circuitry. No moving parts, nothing visible happening. Supposedly a quantum dot light source should be lossless, other than the losses thru the led driving it. Way solid state.

stonehold said:

Originally 'solid state' ment non-tube/relay/dohickey based circuitry. No moving parts, nothing visible happening. Supposedly a quantum dot light source should be lossless, other than the losses thru the led driving it. Way solid state.

Click to expand...

Thanks for that! I 've spent a bit of time trying to answer that question in my head (in the context of this news).

'Solid state electronics' refers to electrons flowing throw solid semiconductor materials as opposed to vacuum/gas filled tubes. High powered LEDs typically use indium gallium nitride or indium gallium arsenide semiconductor materials.

White LEDs are currently made using a phosphor on top of a blue LED. The article http://www.ashlandcitytimes.com/apps/pbcs.dll/article?AID=/20061206/NEWS0201/612060431/1291/MTCN01 is refering to an alternative method to using this phosphor. There have been several articles refering to nano-grooves quantum dots etc. for improving LED efficiency. It's all very confusing.

The above article doesn't really go into any detail about how this can be applied to LEDs. This article does: http://www.evidenttech.com/applications/quantum-dot-ssl.php in summary: The quantum dots can be used to alter the wavelength of the light emitted from the semiconductor. This replaces the phosphor and results in higher efficiency and also the potential to tune the wavelength of the emitted light as desired resulting in a better light spectrum.

The news here is that this quantum dot technology produces WHITE light directly.
No need to mix different phosphors in an RGB emitting paste.

The main thought that I took away from those articles is tunable (custom-sized) bandgaps. And then mixing bandgaps for red, green and blue to produce white light. It all looks very cool.

I wonder why they don't use nonlinear crystals like PPLN for frequency doubling an infrared LED. Novalux uses this technique for manufacturing an RGB laser as the core of a video projector and they have acheived 32% overall efficiencies, not to mention obtain over 1500 lumnes from a device no bigger than one inch in size.

This looks to be exactly the same thing they made a big hub-bub over last year.

From another thread over a year ago:

"Another story with photos and a much better description:

http://www.sciencenewsdaily.org/story-7421.html

http://exploration.vanderbilt.edu/news/news_quantumdot_led.htm

FYI, Sandia and others have been fiddling with quantum dots for light. Sandia had a story on this at least two years ago.

They are real, and provide much promise, and this fella looks to have accidentally blundered into the JackPot/HolyGrail of quantum dots, like an ignorant oaf.

These sorts of things happen on occasion, and is great news. Even better is the common cheap materials they made those dots from. YAG:Ce is what the LED phosphor is called, but whats in it? Rare Earth Cerium-doped yttrium aluminum garnet (there is a mouth full).

The study estimated that wine consumption in the United States would grow by 28.6 percent from the 2003 figure to 27.66 million hectolitres (7.19 billion gallons) in 2008.

The quantum dots are made from cadmium selenide (CdSe) nanocrystals, which are what photocells/NiCd/some types of solar cells/some types of rectifiers/xerographs, use, and is used in all sorts of products that sense light, as well as vulcanizing agents. So Cadmium and Selenium are rather common, so this type of quantum dot materials are low cost too.

Not that each LED uses much phophor anyhow, the entire Luxeon cost them under 0.25ea to actually make. This huge profit margin LumiLEDs has climatized the market to, is one area that I am very excited to see competition in, to get the prices down significantly. The rumor mill has it, that high power LEDs should fall to 1/2 their current price within the next year. This isn't due to cost reduction in the production, just competition in the market.

Unfortunately, LumiLEDs has the most expensive packaging on the market, and is also very process intensive. But they aren't down to the pricing levels yet, where different high power LED packages make much difference in the profit margins.

BTW, here is the link for the original paper. If anyone is a member of ACS, or can somehow snag this, I'd sure be interested in reading it!!!!! Please PM me if you can snag it!
http://pubs.acs.org/cgi-bin/abstract.cgi/jacsat/asap/abs/ja055470d.html
"

The thread:
https://www.candlepowerforums.com/threads/96088&highlight=quantum

frenzee said:

I wonder why they don't use nonlinear crystals like PPLN for frequency doubling an infrared LED. Novalux uses this technique for manufacturing an RGB laser as the core of a video projector and they have acheived 32% overall efficiencies, not to mention obtain over 1500 lumnes from a device no bigger than one inch in size.

Click to expand...

According to their press releases, just the conversion to red looks to reduce the efficiency down to 25% which puts it basically equal to the CREE XR-E. I'm not sure what the efficiencies drop to for the blue and green.

Where did you find the 32% number?

Yep! Same thing. So this is old news...

I wonder what happened since then.

NewBie said:

This looks to be exactly the same thing they made a big hub-bub over last year.

Click to expand...

NewBie said:

Where did you find the 32% number?

Click to expand...

http://www.novalux.com/assets/downloads/NECSEL_Arrays_Apps.pdf

Page 2, paragraph 3

Ah, it looks like the source is 32%?

Figure 4 shows the average power vs. total peak current (200 ns at 500 kHz) of 800 mW for a 15-element array. Total power efficiency (532-nm output power/electrical power into the array) was almost 5%.

It is expected that with expected improvements, power efficiency will exceed 10% for frequency doubled array devices operating in the blue (460-nm), green (532-nm) and red (620 to 635-nm).

NewBie said:

The study estimated that wine consumption in the United States would grow by 28.6 percent from the 2003 figure to 27.66 million hectolitres (7.19 billion gallons) in 2008.

Click to expand...

This was a test to see if we were all paying attention, right?

Skibane said:

This was a test to see if we were all paying attention, right?

Click to expand...

hehe, I caught that too. I was waiting for the connection -- perhaps quantum dot LED's were used together with rare earth magnest to fix Beaujolais Nouveau? (I don't know about the rest of you, but IMO that stuff is paint thinner.)

Okay, so the laser guys are at 5% and hope to get to 10% in the future, and Skibane is thinking about alcohol...or was he thinking someone drank too much?

I wonder if alcohol and lasers mix...

Ah, there we go:
With alcohol lasers, such as CH3OH
http://ftu.frascati.enea.it/diag/twocol.html

Or:

Use of low-energy laser as adjunct treatment of alcohol addiction
http://www.springerlink.com/content/medy862lft11m6hj/

I think this a very good & interesting development.

Don't get me wrong, I luv LED's... but you've got to admit the quality of the 'white' LEDs leaves a bit to be desired aesthetically. It's a very harsh and artificial light. I believe most white LEDs use a combination of phosphors to get somewhat white light from a blue LED. No wonder when I use many of these LED lights it reminds me a reading a book using the light from a CRT.

Our eyes evolved to work under an incandescent light source - the sun. I've always considered good incandescent lighting to be the benchmark for pleasing artificial light. Unfortunately it's not very energy efficient... most of the energy is radiated as IR. Apparently this quantum dot recipe produces a pleasing continuous spectrum which approximates a blackbody source better the weird spectral curves one gets using LEDs + phosphors. Even if you loose a little efficiency.

Here's another link on it:
http://www.ascribe.org/cgi-bin/behold.pl?ascribeid=20051020.101337&time=10 22 PDT&year=2005&public=1

The quantum dot stuff is very interesting. What they are finding is that structures smaller than the wavelength of radiation being manipulated (for visible light this would be structures up to 100's of atoms across) lead to many interesting effects - such as getting more than one electron emitted per photon absorbed (could lead to more efficient solar cells), continuous spectrum from a narrow source (here), or even lenses with a negative index of refraction.

NewBie said:

Ah, it looks like the source is 32%?

Figure 4 shows the average power vs. total peak current (200 ns at 500 kHz) of 800 mW for a 15-element array. Total power efficiency (532-nm output power/electrical power into the array) was almost 5%.

It is expected that with expected improvements, power efficiency will exceed 10% for frequency doubled array devices operating in the blue (460-nm), green (532-nm) and red (620 to 635-nm).

Click to expand...

You're comparing apples to oranges here. Blue and green lasers use DPSS tech, while red lasers are just the diode ('direct injection'). Direct injection laser diodes, in the higher powers, have the highest quantum efficiencies of any light source. Some have conversion efficiencies of 60-70%.

The problem is visible direct injection laser diodes are only available on either end of the visible spectrum - red or violet. In order to get other colors (green or blue) you still need to use DPSS tech, where an IR laser diode gets converted to visible light using a crystal set. So the overall efficiency of these lasers is much lower than the diode itself.

For example, see nlight on the efficiency of their high powered LD's
(products->publications->white papers)
http://www.nlight.net/publications.html

Even the low power red diodes (635 nm) in my pointers had quantum effiencies approaching 20% - good but unremarkable for a laser diode.
http://candlepowerforums.com/vb/showthread.php?t=140955

LEDs are keen, laser diodes are keener

I'm just looking at their .pdf, and their claimed efficiencies.

Looks like lots of work to come.

You see a lot of this type of thing in the display industry, very little ever makes it to market, unfortunately.