Change the emission wavelength of an LED?

[mindlessmalk]

I am looking at a specific UV LED:

" 5mm Ultra-violet LED. Emits blue 395nm UV light. Water-clear lens. 3.7 Vdc, 20 mA. 30 degree beam pattern. Ideal for counterfeit bill detection, detection of fluorescence in minerals, black-light light poster lighting. "

I want to be able to "tune" the LED into a specific wavelength.
I want to be able to use it for Longwave and Shortwave UV Light.
Currently this LED operates in the Longwave end.

Can you alter the wavelength of an LED by altering the current?

Would i need to have a dual-color LED to do that?

I may be way off here...
Thanks!

Nate

 

[dknguyen]

It's the atomic structure of the semiconductor material that determines the colour of the LED, therefore I do not think you can tune it. It is set in stone (or matter) so to speak.

You could probably filter out the desired wavelengths from a single LED though, if it initially emitted those wavelengths.

 

[Torben]

Nope, dknguyen is right--you're stuck with the wavelength the LED in question was designed for.

That said, you *can* get different wavelengths out of LEDs by running too much current through them. You'll have to change the LED every few seconds though, as the weird colours they give off are soon replaced by smoke. I've gotten some pretty orange tones from red LEDs this way. Then they quickly became DEDs (dark-emitting diodes).


Torben

 

[crust]

Perhaps there is an LED material that has the bandgap you want. If you want to go deeper UV then you need a higher energy bandgap. I don't know if they exist, b/c you did not mention what wavelength you wanted. For lasers, deep UV is a pain. There is as of yet no material that lases at those deep UV (266nm) wavelengths. As a result, you usually have to use a 1066nm source, than you double to 533nm then you use a crystal that basically takes two photons in and output 1 photon with twice the energy (and consequently half the wavelength) to get 266. I think the last time I worked with one it drew 2000W of power to generate 150mW of UV. It also had a dessicant pump and a chiller to keep the crystal resonator at a consistent temperature. I can't remember the per hour cost of running it, but it was fairly hight.

 

[mindlessmalk]

I think that 300-400nm would suit my needs. I don't need it for any sort of laser, I am just testing a little mineral fluorescence. I was thinking that i could just get one type of LED for both long and short wave UV. I dont need anything on the germicidal scale(250<nm).
Thanks for answering the question!

 

[crust]

I see, I misunderstood, what I thought is that you wanted to have a system that is outputting UV at a specific wavelength that was different than the LED you had. Now that I see your response, what you want is to be able to arbitrarily set the wavelength. Not going to be possible with an LED that will work at all the wavelengths you listed. I am not even sure filtering a UV source (not an LED) would be able to do all those, maybe.

 

[petrv]

Yes, the wavelength of a LED is fixed, what about using a few of them with different wavelengths and switch them as needed ? If you are looking for LEDs with unusual wavelengths for sale have a look here:

http://www.roithner-laser.com/

Petr

 

[ericgibbs]

hi,
Is a 'broadband' standard UV light, using optical bandpass filters acceptable or are you looking for a more 'mobile' UV light source.

 

[Torben]

hi,
Is a 'broadband' standard UV light, using optical bandpass filters acceptable or are you looking for a more 'mobile' UV light source.

That's what I was thinking--maybe a water filter UV lamp with some filters. I don't know if they put out enough of the required wavelengths, though.


Torben

 

[Boncuk]

Hi Nate,

a wave length of 300nm is already very dangerous if that light hits your unprotected eyes and causes more damage than looking directly into the arc of an arc welder. They do produce 340nm UV-LEDs (UV-A) at Seoul semconductors, but for a horrible price of 53US$ per piece if your order is 100pieces at least.

You can however purchase UV-LEDs emitting at 400nm for a reasonable price of US$ 1.96. Check out https://www.reichelt.de and search for: LED 5MM UV.
Look at the left hand top corner where is says "Suchen" and put in the info.

The price given is EURO 1.40 including sales tax. Delivery to foreign countries is sales tax exempt.

General remark: Trading with UV-LEDs emitting shorter wave lengths than 400nm is strictly limited for medical applications in Europe. Maybe the same applies for your country.

Hans

 

[crust]

Perhaps OP can clarify ... Do you want an adjustable UV source, iow, do you want to be able to sweep the frequencies? Or is it a fixed set of frequencies you desire.

300nm is dangerous, so is 266 especially at the power density of a laser. On our 266 laser, putting flammable objects in the beam causes them to combust almost instantly. To find the beam, I use an index card that I colored with highlighter. We also have UV detector cards but they are expensive and like 1/8 the size of an index card.

I don't know about the restrictions here, the one we use is the Coherent Azure. The other one I used which is way easier mainly because it does not have a resonant cavity is the 355nm I can't remember who makes it though.

 

[Hero999]

I thought they used gas based lasers for UV not LEDs.

395nm is just about visible will and is a deep violet in colour, it will also have some blacklight capability but isn't very good. You can buy LEDs that output 370nm but they are very expensive.

RS components used to sell small blacklight lamps the size of neon lamps which can be powered from the mains by adding a series resistor or a small battery powered inverter. I don't know if they still make them as RS discontiniued them a few years ago.

 

[crust]

They can use gas lasers for UV, but there are have been so many advances in solid state lasers that they have taken over in certain critical segments. Now that I am thinking about it, we also had a q-switched deep UV laser that was tunable with a coherence length of only a couple of cm. It was a close cousin of the tattoo removal lasers (but higher power). It used water cooling and flashlamps.

 

[ikalogic]

maybe some couloured lenses alter the frequency, no?

(i am absolutely ignorant in this field! but i've seen a documentary about that from some time...)

 

[crust]

No, the filters just attenuate or pass certain wavelengths. The wavelengths have to exist in the source first.

 

[mindlessmalk]

Sorry for the delay. Thanks for all of your posts.
I am looking to embed LEDs of just the right wavelength into a bed of Quartz, and other fluorescent minerals. First i wanted to make some sort of device that i could find the optimal fluorescing wavelength of the various minerals. I have found charts online, but they only give a broad range. See this: **broken link removed**
Most minerals are divided into long and short UV wavelengths. From what I understand long and short are in two broad ranges of the UV spectrum. 400 nm - 315 nm for long, and 280 nm - 100 nm for short.
If the shortwave LEDs are going to be too much of a hassle to get, then i will just stick with the longer wavelengths.
Would the germicidal LEDs still hurt your eyes looking only at the fluoresced mineral, or do you have to be looking right at the LED source?

Anyway, I suppose I should just get some cheap long wave UV LEDs and see which minerals I can use with them.

Thanks!
Nate

 

[Boncuk]

Changing the wave length of an LED

Hi Nate,

a friend of mine living in California is a gem collector and he uses a small incandescent lamp to find out what kind of minerals he found.

Since the minerals reflect the light into many directions those partial reflections should not do harm to an eye.

However be careful not to stay too close to the mineral being "illuminated".

Hans

 

[YannisK]

Hi all, I am new to the site and my question is, if you have a typical smartphone LED wavelength (white light), could you change it to become infrared for a limited amount of time (say 1-2 mins?

Cheers

Y