UV LEDs for UVA, UVB & UVC | Opsytec

Production of ultraviolet light-emitting diodes

Electromagnetic radiation is generally generated in III-V semiconductors, i.e. semiconductors made of elements from the third and fifth main groups of the periodic table, whereby the wavelength of the emission peak of UV LEDs is primarily determined by the solid solution composition of the material.

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By alloying the semiconductors aluminum nitride (AlN), gallium nitride (GaN) and indium nitride (InN), emission wavelengths in UVA (400 nm - 315 nm), UVB (315 nm - 280 nm) and UVC (280 nm - 200 nm) can be achieved.

The production of UV LEDs involves a number of steps: 
Design of the LED heterostructure and chip layout, growth of the substrates and base layers, epitaxy of the semiconductor heterostructure, processing of LED devices at wafer level and finally the separation of the wafers into LED chips and their assembly in packages. UV LEDs therefore consist of many hundreds of semiconductor layers whose composition and doping must be adjusted according to the respective functionality.

The emission wavelength of the LEDs is determined by the composition and doping in which the UV radiation is generated. For all steps, it is important that the electrical power is efficiently converted into optical radiant power. The wall-plug efficiency (WPE) is a particularly important parameter for the application. A key parameter for the application is the overall efficiency, referred to as wall-plug efficiency (WPE). The overall efficiency of UV LEDs indicates the ratio of the optical radiant power to the electrical power supplied.

UVA-emitting UV LEDs now achieve a WPE of around 30-40 %, while blue-emitting LEDs already achieve a very high WPE of around 80 %. In contrast, LEDs with emissions in the low UVB and UVC range have significantly lower WPEs of less than 5% to 10%. For this reason, UVB and UVC LEDs are subject to continuous optimization and technological development. As a result, available LED types have to be replaced by successor types after some time.

Comparison of UV LEDs for UVA, UVB & UVC

Compared to older UV LEDs, the latest UVB and UVC LEDs show significantly higher efficiency and improved performance. Older UV LEDs often suffered from high operating temperatures and rapid degradation, which has been significantly improved by the latest developments. The current generation of UVB and UVC LEDs utilize advanced cooling technologies and improved semiconductor structures and optical couplings that not only extend lifetime but also increase efficiency.

UVB and UVC LEDs do not yet achieve the performance and output of UVA LEDs, but have been able to catch up significantly in recent years.

UVB and UVC LEDs as well as UVA LEDs are manufactured from different substrates and by different epitaxy processes that are specifically tailored to the desired wavelengths and performance requirements. The choice of substrate and epitaxy method has a significant impact on the efficiency, performance and cost of the LEDs.

A technical comparison between UVA LEDs with wavelengths of 365 nm and 385 nm and UVC LEDs with wavelengths of 265 nm, 285 nm and 295 nm is shown below. This table takes into account general parameters such as efficiency, output, service life and typical applications.

Applications of UVA LEDs

UVA LEDs with wavelengths in the 315 to 400 nm range are used in numerous technical, scientific and industrial fields, playing a central role in non-destructive testing (NDT) and many other innovative applications.

Non-destructive testing (NDT): UVA LEDs are an important tool in fluorescence testing, a sub-area of NDT. They are used to visualize surface defects or differences in materials by exciting fluorescent dyes that are applied to the parts to be tested. This method is commonly used in the aerospace, automotive and metalworking industries to identify cracks, overlaps, pores and other imperfections.

UV curing: One of the most common applications of UVA LEDs is the UV curing of paints, adhesives and coatings. This technology is used in the printing industry, in the manufacture of electronics (e.g. when bonding smartphone screens) and in the dental industry. UVA LEDs offer the advantage of fast and targeted curing, which shortens process times and increases energy efficiency.

The photoinitiators that have been used in UV curing and UV printing for some time are specially designed to react to the corresponding UVA wavelengths. Additional irradiation with UVB light in the 280 to 300 nm range can improve the curing process.

Medical applications: In dermatology, UVA LEDs are used for phototherapy, particularly for the treatment of skin conditions such as psoriasis and eczema. UVA radiation can help to reduce inflammation and alleviate the symptoms of these diseases.

Plant growth and horticulture: UVA LEDs play a role in agricultural technology, particularly in artificial lighting for plant growth in greenhouses. They can help control certain growth processes and increase plant resistance to pests. Irradiation with UVA causes plants to shorten in length.

Forensic applications: In forensic science, UVA LEDs are used to visualize biological traces such as blood, semen or other bodily fluids. This technique is also used to identify forged documents or banknotes.

Analytical applications: In chemistry and biochemistry, UVA LEDs are used to analyze substances by fluorescence spectroscopy. This method makes it possible to precisely determine the composition and concentration of chemical compounds.

Applications of UVB LEDs

UVB LEDs are increasingly being used in medicine for the treatment of skin diseases such as psoriasis and vitamin D synthesis. Alternatively, excimer lamps or lasers with a wavelength of 308 nm have been used in dermatology for many years. UV LEDs are slowly replacing classic UV lamps. The other applications are therefore:

Vitamin D production: UVB radiation is crucial for the natural production of vitamin D in the skin or food. UVB is used in devices to produce vitamin D, vitamin D2 or previtamin D3. When UVB light with a wavelength between 290 and 315 nm hits the skin, the B-C ring structure of the 7-DHC molecule is broken down. This process is called photolysis.

Unlike humans, who synthesize vitamin D by exposing the skin to UVB radiation, plants do not produce vitamin D in the same way. When fungi and some algae species are exposed to UV radiation, the ergosterol present in their cells can be converted to ergocalciferol (vitamin D2) by a photolytic reaction similar to that which occurs when vitamin D3 is synthesized in human skin. UVB radiation breaks specific bonds in the ergosterol molecule, which leads to its conversion into previtamin D2. Similar to the synthesis of vitamin D3 in humans, the unstable previtamin D2 is converted into the stable vitamin D2 through heat-dependent isomerization.

Tanning: In the cosmetic industry, UVB LEDs and UV lamps can be used in tanning devices to achieve an even and controlled skin tan.

Phototherapy: In medical treatment, UVB is used for phototherapy, particularly for skin conditions such as psoriasis and vitiligo. UVB radiation can help to normalize the overactive skin cells and alleviate the symptoms of these diseases.

Plant cultivation: UVB LEDs also have applications in plant breeding, as UVB light affects the growth, flowering time and secondary metabolites of plants. Irradiation with UVB light can help to increase the production of certain plant constituents such as vitamins, aromas and colorants.

THC production in cannabis: A specific application of UVB LEDs is the optimization of THC production in cannabis. UVB radiation is known to increase stress in plants, which in turn can increase the production of secondary plant compounds such as THC. This is particularly used in legal cannabis growing environments to improve the potency and quality of plants.

Material testing: UVB is used in accelerated aging testing of materials to simulate solar radiation and evaluate the long-term stability of plastics, paints and other materials.

Applications of UVC LEDs

The progressive development of UVC LEDs in terms of efficiency, durability and cost makes them an increasingly attractive option for many areas where mercury vapor lamps have traditionally been used. Therefore, the general applications are:

UV disinfection: one of the most prominent uses of UVC is the disinfection of water, surfaces and air. UVC radiation is highly effective in inactivating bacteria, viruses and other microorganisms, as it damages their DNA or RNA and thus prevents them from reproducing.

UVC LEDs are used in compact water treatment systems to remove pathogenic germs from drinking water at the point of use, i.e. the tap.

Surface disinfection: In hospitals, laboratories and in food processing, portable or permanently installed UVC devices are used that emit UVC radiation to sterilize tools, packaging and work surfaces. Alternatively, UVC lamps are integrated into air conditioning and ventilation systems to clean the air of germs and prevent the spread of disease.

Wound care: UVC LEDs will also be used in medical treatment and wound care in the future, particularly for treating hard-to-heal wounds and infections. The application of UVC light to infected wounds can inhibit the growth of bacterial pathogens and promote healing. It is important to dose the radiation precisely so as not to damage the skin.

Direct photopolymerization: UVC is ideal for photopolymerization, a process in which light-sensitive resins or liquids are cured into solid polymers by irradiation. In additive manufacturing, known as 3D printing, UVC enables the fast and precise curing of photopolymers, resulting in detailed and solid 3D printed objects.

In the manufacture of printed circuit boards and electronic components, UVC light is used to cure adhesives and coatings that are critical for stability and functionality.

Other analytical applications:

UVC LEDs serve as light sources in spectroscopy, where they are used to analyze chemical and biological samples, such as u fluorescence or absorbance measurement in environmental monitoring.

Substrates & epitaxy for UV LEDs:

• UVA LEDs (320 nm to 400 nm):

Sapphire (aluminum oxide) is often used as a substrate as it is inexpensive and readily available. Other substrates such as silicon carbide (SiC) or silicon (Si) are also in use to take advantage of thermal conductivity and compatibility with existing semiconductor manufacturing technologies. The epitaxial layer is deposited by Metal-Organic Chemical Vapor Deposition (MOCVD) and typically consists of aluminum gallium nitride (AlGaN), with the aluminum content being adjusted depending on the desired emission.

• UVB LEDs (280 nm to 320 nm) and UVC LEDs (100 nm to 280 nm)

The same substrates are often used for UVB and UVC LEDs as for UVA LEDs, but the requirements for material quality and purity are higher, especially for the shorter wavelengths in the UVC range. Alternatively, native substrates such as aluminum nitride (AlN) are also used, which enable a better grating match and therefore lower defect densities. AlGaN is also used here as an epitaxial layer, but with a higher aluminum content in order to achieve the shorter wavelengths. The epitaxial layer is also formed using MOCVD, whereby particular attention is paid to the control of defects and the homogeneity of the layer.

Hello All,

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I am fairly new to the 3d forums, and the company I work for has recently decided to invest in a 3D printer. Our first step into the 3d printing world has begun with Formlabs, and I am here to share our results with the community! Below are pictures of our 3d Print room and the the UV cure-box that has been built.

3D Print Lab:

The room has been fitted with:

• two wall cabinets that have an open-bottom section that serves as a display for the prints.
• a high work table that holds the finishing kit and a Dremel workstation
• a metal peg board for easy access to tools.

The Form 2 Printer sits on a rolling cabinet. This is ideal when any maintenance needs to be performed however the drawback (pausing the print before opening a drawer) can get annoying, but it is a small price to pay. The room serves dual functionalities of not only being the 3d print-lab for the company, but also a showcase room for new technologies for visitors in the building. Additional items still needed to complete the room are a dedicated computer and a large monitor screen.

UV Cure-box:
Since the company dedicated an entire room for this equipment, I built a professional-looking UV cure-box while not spending absurd amounts of money.

Equipment needed:

• Soldering iron w/ solder
• Wire shrink tubes
• 405 nm led strip (non-waterproof)
• AC power supply that will work with the LED strip (12V, 5A max, 60Watt max is the one i used)
• Wire w/ wire strippers
• Wire to power supply connector (green/black in the pictures)
• LED controller with remote (optional)
• Aluminum foil lining (Al sheet-metal typically used for building was used in the box, but store bought Al foil will work just fine) [may need to use 2 or 3 layers if the foil is thin]
• 3m double sided tape
• threaded rods
• clear glass or clear plastic sheet
• Plastic-Storage container
• Drill machine

Step 1: Measuring/ Figuring-It-Out
find:

• location of threaded rod holes
• how you will route your LED strips and wires
• location of holes for wire routing
  Your LED strips will need to be attached in a SERIES connection. I have mine starting at the bottom of the container and ending at the top [power supply at the top].

Step 2: Base Layer

• Drill holes for threaded rods (make sure threaded rods will be evenly horizontal)
• Drill holes for any wire routing
• Attach double sided tape to the side walls, bottom, and underside of the lid (leave the outward facing protection strip of the tape on)

Step 3: Aluminum Foil

• Attach Al Foil → Do the sides first, then the bottom, then the underside of the lid. Make sure to leave enough room on the underside of the lid so it can shut properly. When doing this step its best to remove the the protective film on the tape as-you-go instead of removing it all at once.

• re-drill holes if the AL foil is covering any holes

Step 4: LEDs

• You should have a basic idea of how you will position your LEDs at the point.

• [Go section by section for this step. Start at the bottom, then sides, then underside of the lid]

• WIRING should be done in SERIES

• Cut LEDs to appropriate length.

• Attach wires with wire shrinks (precautionary measure so it does not short-circuit) to the LED strip contact points.

• Attach double sided tape to underside of the the led strip and attach LED to the foil.

• Use double sided tape to hold down any dangling wires firmly against the walls

Step 5: Check and Final Check
- Hook the “wire to power supply” connector to the wires first then the power supply and check all LEDs are working.

• Attach threaded rods
• Attach the nuts to the ends of the rods and lay the clear plastic sheet on top of the rods
  - Do a final check, and if everything works you are done!

notes:

• The box does take some time to heat up, so a solution is to turn it on in the morning and let it heat up a little bit before using. To speed this up use a hair dryer on low setting and gently heat up the interior of the cure box.

- Use EXTRA long wire for the LED connection between the lid and the main container. This way you can take the lid fully off and let it sit somewhere without having to worry about ripping apart your LED-to-LED connection

If you have any comments or suggestions please post below.
Thanks!

Unless those are really high wattage LEDs, you’re probably going to want more of them than you have. Curing wants lumens and candlepower decreases with the square of distance. Your box is large which is nice, but the LEDs are much further away from the center as a result. You need more lumens to make up for distance.

Also, some resins (Flexible) need to be post-cured underwater (anaerobic environment). If you used a clear container you could put the LEDs on the outside and fill the inside with water when/if you needed to.

You’ve seen my post here? Check out how much closer each wrap of LEDs is on my design. The amount of light I’m getting on the print inside the jar is just getting the job done. Further away and spread out more, I would not have enough light.

Also. You appear to be using a RGB programmable LED string. This may not be doing what you expect. The “color” of the light is not what’s important, it’s the actual frequency of the light. That will exclusively be a function of the frequency of the Blue LEDs on the LED string. Unfortunately, the frequency you need (405nm) is almost purple in color. It’s unlikely to be the frequency of the LEDs on your RGB string. An RGB LED’s blue LED will typically be in the 470-480nm range. That’s too high to be effective at post-curing (if it has any effect at all, it may not).

The LEDs I recommend in my post are spec’d to output 385-405nm. They’re much closer to the 405nm target but are probably on average a little under. But 470nm will be a wavelength too far.

Thank you for your comment,

I have re-looked over the stats of the LEDs and they are not RGB, but a UV 395-405nm (near blue/purple). Perhaps the controller made it look like RGB LED strip? I will have to test out the Flexible underwater curing as I have not printed enough flexible prints to be knowledgeable in that section. Thank you for the reminder/suggestion!

I have been using this box for nearly 2-3 months on a regular basis now and have had no problem curing my prints, but i do need to find a way to get more heat into the box to decrease curing times. I was thinking about introducing a heating element with a fan and have a cut-off at a certain temperature, such as the one below.

The Al sheet metal as opposed to the Al foil you used in your box is able to hold the heat a lot more and also be reflective at the same time.

I do like your clear container for underwater curing however very nicely done!

I used an old microwave oven as the enclosure, took out the magnetron, transformer and other bits that weren’t required, fitted 3 x 10W 405nm LED arrays and used a low wattage (350W) hair-styling hot air brush blowing into the cabinet. Temperature is controlled by a PID controller and Pt resistance thermometer (both a bit OTT - a simple thermostat would have done).

The microwave as enclosure has some advantages: 1) You can pick one up from a dumpster. 2) Rotating glass turntable is easy to clean and helps even out UV exposure 3) Front-loading door is convenient for loading and if you use the interlock, the LEDs and heater switch off automatically when you open the door.

Temperature can get to about 75C maxed out with this set-up - though I obviously don’t run that high!

I have located the following listing on Ebay. The item number is . It is listed as a dry heat UV sterilizer. The seller (china) has responded that the heat setting is adjustable. I am waiting now to hear back what the min and max temp settings and and what type of UV bulb type and the nm rating to see if this would be good for 3D prints. The size internally is about as large as the build space on the Form2, so this might just be a good affordable curing solution. I will let you know the updated info when I receive it. On the listing it shows the unit set for 60C so I am very interested in it.

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