First Ultraviolet Quantum Dots Shine In an LED 47
ckwu with word that South Korean researchers have created the first UV-emitting quantum dots, and employed them in the creation of a flexible LED. Their achievement is notable because
no one has previously succeeded in making quantum dots capable of emitting light at wavelengths shorter than 400 nm, which defines the upper range of the UV spectrum. Writes ckwu: To get quantum dots that emit UV, the researchers figured out how make them with light-emitting cores smaller than 3 nm in diameter. They did it by coating a light-emitting cadmium zinc selenide nanoparticle with a zinc sulfide shell, which caused the core to shrink to 2.5 nm. The quantum dots give off true UV light, at 377 nm. An LED made with the quantum dots could illuminate the anticounterfeiting marks on a paper bill. The article names a few applications of the technology, besides, including water sterilization and industrial applications.
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Water sterilization is the big thing here (Score:5, Informative)
Water sterilization is, I think, the single most important application for this. Current UVs for sterilizing water (I work with these) are still bound to using fluorescent lamp technology. It's bulky, requires a way of way of keeping a thin glass lamp separated from the water but still shining through it (we use quartz sleeves: major $$$), and requires constant maintenance (usually annual or biannual bulb changes, more $$$) and requires an external ballast to operate the lamp (even more $$$$). Cheap, easily cleanable plumbing fixtures that just plug in to sterilize water would be a major win both in cost of clean water here at home and in provisioning to developing nations.
If you're wondering what the scope of the applicatoin is, if you're drinking out of a municipal water supply right now it is probably both chlorinated and UV treated.
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What level of luminescence and at what frequency do current UV sterilizers need to be for current treatment systems? And what wattage/gal are we talking about here? If they can find a way to mass produce these, there could be some significant wins globally for water sanitation.
Also: would this make it possible to create portable systems that you could carry with you whle hiking/carry to remote locations and operate via solar power/battery?
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carry with you whle hiking/carry to remote locations and operate via solar power
It would be difficult to beat the existing system on price: PET bottles. [wikihow.com]
Re:Water sterilization is the big thing here (Score:5, Informative)
The NSF standard, which is the gold standard for UV sterilization, currently requires an irradiation of 40 mJ/cm2. It works best at wavelengths around 250nm, which is still considerably tighter than the LEDs developed in this research.
Yes and no (Score:4, Informative)
Generally speaking, yes... so long as you are still within the effect range.
The germicidal effect comes from an absorption band in DNA. This is (like everything else) a bell curve, where the effect drops off either side of the peak.
This diagram [uvit.co.uk] is a good visual.
Note that commonly available UV emitters (including UV lasers and LEDs and the quantum dots mentioned in the article) are so far out of the effective range to be completely ineffective.
And anything that is effective is pretty dangerous to use, so be careful taking one apart.
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"Note that commonly available UV emitters (including UV lasers and LEDs and the quantum dots mentioned in the article) are so far out of the effective range to be completely ineffective."
Bullshit.
http://www.hexatechinc.com/uv-... [hexatechinc.com]
http://www.cisuvc.com/ [cisuvc.com]
http://www.ledsmagazine.com/ug... [ledsmagazine.com]
I was playing with UV-C LEDs from Nichia years ago that worked just fine for sterilizing water. It's still in use keeping algae from growing in my aquarium.
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I'm flattered that you're reposting my links from below, but I think you're missing GP's point. None of those three links appear to describe units that are "commonly available" -- in one case, it's only engineering samples, and in none of the links do they say a word about pricing or actual availability (the last one claims "mass production", but doesn't back it up).
"UV lasers" are mostly 405nm, not really UV, and the quantum dots from TFA are firmly in longwave territory. So, GP's points stand.
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used for that, you would be better off using a light behind a fan, and feed the exhaust to a old nylon sock. spray the sock with alcohol before you empty it. skeeters can't fly against a wind, so they head towards the light, and get trapped. the alcohol kills them by dehydration. This method kills a local population fairly effectively.
https://www.google.com/search?... [google.com]
About 264 nanometers (Score:5, Informative)
Peak effectiveness for sterilization is around 264 nanometers. DNA has a specific absorption at that wavelength, so light at this frequency destroys DNA.
This wavelength is in the UV-C band, which is the radiation blocked by the ozone layer, which is one reason people are concerned about ozone: it protects us from DNA-damaging radiation.
Mercury emits UV at around 254, which is close enough to the DNA absorption peak to have good effect. A fluorescent bulb without phosphor and UV-transparent glass will work.
The wavelengths cited in the post, 377nm, are too long for germicidal effect. If the work can be extended, it would result in much more efficient germicidal bulbs by generating wavelengths closer to optimal, and because quantum dots are generally very efficient.
You can get UV bulbs for your furnace that stick into the plenum and disinfect the air as it blows past. You might be able to run one of these from an inverter while hiking. Be sure to cover the bulb and be *very* careful not to look at it when it's on.
Re:Water sterilization is the big thing here (Score:4, Insightful)
It's amazing how big of a global impact you could get, from what seems at first glance to be an everyday iterative improvement to an esoteric technical product. Thank you for sharing!
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Could this sterilization tech beat the Steri-Pen for portability, for the outdoors market?
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"UV lightsources are required for the highest quality white LEDs, as the fluorescents only downconvert to longer wavelengths, so the white quality is limited by the pump wavelength."
No, we do just fine with 420nm blue LEDs as the base. Cree's latest 300+ lux/w white LED uses a blue LED as its base, not UV.
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Actually, 420 would be a bit too violet for this application. Cree's XR-E emitters seem to use a blue emitter centered around 450nm (pdf) [cree.com], coupled with a yellow phosphor -- blue + yellow = blue + (green + red) = white. That's how most "white" LEDs work. If you used a shorter-wavelength emitter, you'd need to downconvert all its output power, losing efficiency. By using a blue emitter, you pass some of the blue light, and downconvert just enough of it to yield the perceived color temperature you want.
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" If you used a shorter-wavelength emitter, you'd need to downconvert all its output power, losing efficiency"
Shorter-wavelength blue LEDs (plus a different LED base made of silicon carbide) is how Cree is getting 300+ lumens per watt out of a white LED, 5250K at 350mA 3.6V.
An if memory serves correctly, Slashdot one had a story up about how some company developed some new LED from I think selenium that required no conversion phosphor to output white light, within the last year.
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Air Purification as well (Score:3)
They sell UV lights to put in your air handler to keep mold and mildew growth down but the units are expensive and the bulbs need replacement quite often. A long lasting UV source could be built into the units and keep them clean.
Just in time (Score:3)
If development took only a few more years, we wouldn't have paper money to counterfeit.
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Development of the surveillance state?
I think its neither my banks nor my governments responsibility or right to know precisely where I spend my money. Even if I trusted my government, I don't want shops to know my name or account ID, this would be the ultimate tracking for them. But I guess they are already developing face recognition based approaches that match my face with internet footage (like data bought from facebook) to get my identification.
I don't like the snooping and control the future has for t
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Have you ever filed a Federal and State Income tax form? If so the government already knows where you work, your income, how many dependents you have, where you live, your age, your marital status, and details about any property you own.They started collecting this information way before there was any electronic information age in all it's various manifestations. And to top it off the government doesn't need a search warrant to access any of this information they have compiled and stored. The IRS makes the
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For tax forms, this form of data collection does make sense. And where you live, your age, your marital status and any real estate or car you own should be already known to several parts of the state. Things like income are basic to know for collecting taxes.
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Even though it would help the government perform surveillance, I think most of the money should be plastic chips with RFID. Perhaps down to 25 cent pieces and up to 5 dollars (or maybe more). Sure, I'd have to swap out my wallet for a change purse, but I don't really carry large amounts of cash with me anyways.
It's nice to have some cash on hand when your cellphone's payment system isn't working.
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Cool, but way overstated. (Score:4, Informative)
We already have robust conventional LEDs that emit high power at comparable wavelengths (considered "longwave UV"). This wavelength is not especially useful for purification and sterilization. For that, you need UVC, in the range of 250nm and below. That's still difficult with anything other than a fluorescent emitter or an arc; solid-state emitters in that range have very low power and short life, at least last time I checked.
The other problem with very short wavelengths is finding packaging materials that will transmit and withstand them over long periods. Even longwave UV will cause materials to deteriorate over the lifespan of a solid-state emitter; UVC is much more harsh.
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lifetime isn't terrible, but not as good as visible LEDs. a 250nm 0.5milliwatt diode costs $350 for quantity of one. unit price for 10000 is still over $50
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"solid-state emitters in that range have very low power and short life, at least last time I checked."
What, a decade ago? The UV-C LEDs keeping my aquarium water algae-free have been in operation for at least five years.
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You put the UV LED inside the water filtration system, in direct contact with the water.
Re:Cool, but way overstated. (Score:4, Informative)
Links, please? Last I checked, UV-C emitting diodes were essentially experimental items, with output power below 1mW, and sky-high prices. Feel free to ridicule me mercilessly if I'm wrong, but please post links; I'm a lot more interested in learning about UV-C emitters than in defending my hypothetical reputation.
This page [hexatechinc.com] crows about UV-C LEDs, but is conspicuously silent about output power (beyond calling it "stable"), availability, or price.
This page [cisuvc.com] claims 5-10mW per device, adding that "limited release engineering samples are available today." The datasheet is mum on device lifespan.
This looks more promising [ledsmagazine.com] -- 10mW per device, 10,000 hour life -- but where are the products, and where are the prices?
Obviously, I could be missing some products that are already shipping. But if you actually have a bank of UV-C LEDs that's been putting out enough power to kill algae in your aquarium for the last five years, it looks like a lot of electronics and physics journals would be interested in hearing from you. And so, as I said, would I.
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http://www.nichia.co.jp/en/pro... [nichia.co.jp] - you can contact them for UV-C LEDs, they'll send you a catalog with the less-often purchased UV-B and UV-C diodes there as well. You can also custom-order UV arrays and such.
Cree quit making high-power UV-C LEDs a couple of years ago. HaSun Optoelectronics has 0.5w+ UV-C LEDs. Yes they are expensive. Almost $80 each.
Seoul Semiconductor (rather Seoul Viosys, a subsidiary that focuses on the UV side of LEDs) has high power UV-C LEDs as well, the S265 and S255, for example.
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It almost seems like you're interpreting "UV-C" to include the range from 360-380nm. There are apparently some results indicating that emitters in this range can be germicidal, if you use enough power and enough exposure time; is that where our disconnect is arising?
The Nichia page you linked lists only longwave emitters, with 365nm the shortest wavelength. I'm sure they have shortwave emitters, and maybe even samples for some of them, but if they aren't listed on the Web site, I'm not confident how much of
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"It almost seems like you're interpreting "UV-C" to include the range from 360-380nm."
No, 100-280nm is what I consider. Don't use Aliexpress, nor Alibaba (first off they can't even properly copy/paste data from their own datasheets. Almost every listing is written by a salesperson, not an engineer.) The GOOD SHIT is hidden directly in paper-only catalogs.
Cree most certainly made UV-C LEDs. I'm one of their primary product testers and have been for getting close to a decade (everyone that liked LEDs was piss
Shine a light on me (Score:2)
Insects (Score:2)
Very interesting. I have an application for this where I'm using 365 to 395 nm older style to attract bugs efficiently. The water sterilization is another important application of this. It could reduce cost and increase component life and reliability meaning better water.
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Come on, give us a few details. Are you collecting the bugs for research or are you using the lights as bait for your backyard zapper? Or are you collecting bugs to feed to your pet iguanas?
That's too tantalizing a statement for you not to tell us a little more.
Arachnids (Score:2)
UV can be used to make scorpions glow in the dark, e.g. http://johnbokma.com/pet/scorp... [johnbokma.com] It also works with some opiliones (harvestmen) and millipedes.
BTW, don't built the one I made years ago. Nowadays one can buy a better UV source online, e.g. UltraFire WF-502B with UV LED.