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First Ultraviolet Quantum Dots Shine In an LED
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.
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.
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.
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.
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 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.