murray@uctvax (07/10/90)
Please could anybody who has actually seen a blue LED write in and talk a bit about its colour? There was one message which seemed to imply they looked a little washed out. Is this in fact so? Also does anybody out there know anything about the possibility of building a LED in ultraviolet? I know about IR LED's, but a UV LED would be useful! Mark Murray Physics Dept | I know you understand what you think I | University of Cape Town | said, but I'm not sure you realise that | Rondebosch 7700 | what you heard is not what I meant. | South Africa | | murray.uctvax@f4.n494.z5.fidonet.org - internet murray@uctvax - uninet
heskett@titan.tsd.arlut.utexas.edu (Donald Heskett) (07/12/90)
The one I bought from Ledtronics (?) has a color that is a sort of 'powder' blue. The light was bright enough, just not a very intense blue. A look at its spectral output curve showed no output in the UV. I was hoping to use it as a sensor in the UV (most LEDs will work as low power photoelectric sensors). I don't have the spec sheet here with me, but I believe the 'blue' end cutoff was at about 470nm. I might mention that these toys aren't cheap. The one I bought cost $15.
larry@kitty.UUCP (Larry Lippman) (07/12/90)
In article <HESKETT.90Jul11122218@mercury.titan.tsd.arlut.utexas.edu>, heskett@titan.tsd.arlut.utexas.edu (Donald Heskett) writes: > The one I bought from Ledtronics (?) has a color that is a sort of > 'powder' blue. The light was bright enough, just not a very intense blue. > > A look at its spectral output curve showed no output in the UV. I was > hoping to use it as a sensor in the UV (most LEDs will work as low > power photoelectric sensors). I don't have the spec sheet here with > me, but I believe the 'blue' end cutoff was at about 470nm. LED radiation emission technology issues notwithstanding, only certain special plastic formulations are capable of transmitting UV radiation without an overwhelming degree of attenuation. Most LED's that I am aware of are encapsulated with epoxy materials that have a usable low end wavelength around 400 nm. While some plastic formulations such as methacrylates can be used as low as 275 nm, I am not aware of any such material being used in LED's, however. It is therefore not surprising that you detected no UV radiation. Larry Lippman @ Recognition Research Corp. "Have you hugged your cat today?" {boulder||decvax||rutgers||watmath}!acsu.buffalo.edu!kitty!larry VOICE: 716/688-1231 || FAX: 716/741-9635 {utzoo||uunet}!/ \aerion!larry
henry@zoo.toronto.edu (Henry Spencer) (07/12/90)
In article <17596.2699d803@uctvax> murray@uctvax writes: >Also does anybody out there know anything about the possibility of building >a LED in ultraviolet? I know about IR LED's, but a UV LED would be useful! If you thought a blue LED was a long time coming, I suggest not holding your breath waiting for UV LEDs. The problems get exponentially worse, so to speak, as the wavelength shortens. -- NFS: all the nice semantics of MSDOS, | Henry Spencer at U of Toronto Zoology and its performance and security too. | henry@zoo.toronto.edu utzoo!henry
gordonl@microsoft.UUCP (Gordon LETWIN) (07/14/90)
In article <HESKETT.90Jul11122218@mercury.titan.tsd.arlut.utexas.edu>, heskett@titan.tsd.arlut.utexas.edu (Donald Heskett) writes: > The one I bought from Ledtronics (?) has a color that is a sort of > 'powder' blue. The light was bright enough, just not a very intense > blue. I have two of these - in the clear and the diffused package. I agree that they're not a deep "violet blue" but I wouldn't describe them as "powder blue". Powder blue has a lot of white in it, I think, whereas these leds don't, obvuiously. Their peak emission is 470 NM, as I recall, so those with the right chart can determine the colour. I'm perfectly satisfied with the blue - it's a "real, true blue", but it's not a super dark "royal blue"... gordon letwin
bwhite@oucsace.cs.OHIOU.EDU (Bill White) (07/15/90)
In article <1990Jul11.233848.29098@zoo.toronto.edu> henry@zoo.toronto.edu (Henry Spencer) writes: >In article <17596.2699d803@uctvax> murray@uctvax writes: >>Also does anybody out there know anything about the possibility of building >>a LED in ultraviolet? I know about IR LED's, but a UV LED would be useful! > >If you thought a blue LED was a long time coming, I suggest not holding >your breath waiting for UV LEDs. The problems get exponentially worse, >so to speak, as the wavelength shortens. My simple procedure for getting UV out of an LED (use yellow, as they are cheaper). 1. Take a power cord. 2. Insert a diode in-line with one lead (after all, you want 120VDC, not AC) 3. Wire up the LED 4. Plug it in. Bingo! You will (briefly) see a blinding white light that contains some UV. Now all you have to do is filter out the visible portion, and find some way of cleaning up the mess you just made (avoid inhaling the fumes). All kidding aside, I actually used to take those micromini clear-cased red LED's (with the two leads coming out axially, they looked a bit like surface mount resistors) and put the leads across a 9V battery. They would glow white! (and burn my finger!) I also wouldn't hold my breath for UV. Hey, if you really want to wait a long time, ask for an X-ray LED (or gamma ray, for that matter) -- | Bill White Internet: bwhite@oucsace.cs.ohiou.edu | | VIQUE'S LAW: | | A man without religion is like a fish | | without a bicycle. |
paul@hpldola.HP.COM (Paul Bame) (07/16/90)
> A look at its spectral output curve showed no output in the UV. I was > hoping to use it as a sensor in the UV (most LEDs will work as low > power photoelectric sensors). I don't have the spec sheet here with > me, but I believe the 'blue' end cutoff was at about 470nm. Selenium (sp?) photo cells have UV response.
rdi@cci632.UUCP (Rick Inzero) (07/17/90)
In article <1551@oucsace.cs.OHIOU.EDU> bwhite@oucsace.cs.OHIOU.EDU (Bill White) writes: >In article <1990Jul11.233848.29098@zoo.toronto.edu> henry@zoo.toronto.edu (Henry Spencer) writes: >> >>If you thought a blue LED was a long time coming, I suggest not holding >>your breath waiting for UV LEDs. The problems get exponentially worse, >>so to speak, as the wavelength shortens. > >I also wouldn't hold my breath for UV... I may have missed a follow-up where my question was answered, but: just what's so technologically difficult here, regarding the UV LEDs? Sure, the currently used plastic housings won't pass shorter wavelengths of UV, but so what? Wouldn't a silica glass housing work just fine, in fact, even passing short wavelengths of UV?? I'm not saying they'd be cheap, but I don't see any big hurdles that need to be leaped. Unless there's some problem with actually generating the UV from the light emitting diode chip itself... So far, all I remember is postings that the plastic housing was the problem. Rick Inzero rochester!cci632!rdi Computer Consoles Inc. (CCI) uunet!ccicpg!cci632!rdi Rochester, NY uunet!rlgvax!cci632!rdi "Your grandmother never, ever called me stupid. She always called me 'pinhead'." -Jimmy Stewart in 1988 Campbells Soup commercial.
whit@milton.u.washington.edu (John Whitmore) (07/18/90)
In article <38692@cci632.UUCP> rdi@ccird3.UUCP (Rick Inzero) writes: > >...just what's so technologically difficult here, regarding UV LEDs? >Sure, the currently used plastic housings won't pass shorter >wavelengths of UV, but so what? Wouldn't a silica glass housing work just >fine, in fact, even passing short wavelengths of UV? The light emission occurs preferentially at the bandgap energy of a semiconductor. GaAs gives infrared; Ga, Al, and In in some proportion with As, P give various shades up to green. To get blue, SiC is used (that's silicon carbide, like the grit in sandpaper). For UV, you'd need to develop yet another (new) semiconductor. Maybe doped diamond? The bandgap is about right for UV... John Whitmore
henry@zoo.toronto.edu (Henry Spencer) (07/18/90)
In article <38692@cci632.UUCP> rdi@ccird3.UUCP (Rick Inzero) writes: >Unless there's some problem with actually generating the UV from the >light emitting diode chip itself... So far, all I remember is postings >that the plastic housing was the problem. That's a side issue; the hard part is getting short-wavelength emissions out of semiconductors at all. (Nondestructively, that is! :-)) It's not a packaging problem that has delayed useful blue LEDs until quite recently. The mechanisms and materials that fairly easily yielded IR, red, yellow, and green simply can't be stretched to blue, let alone further. My impression is that the blue ones are a triumph over major difficulties, and nobody's in a hurry to tackle UV. -- NFS: all the nice semantics of MSDOS, | Henry Spencer at U of Toronto Zoology and its performance and security too. | henry@zoo.toronto.edu utzoo!henry
berryh@udel.edu (John Berryhill) (07/18/90)
In article <38692@cci632.UUCP> rdi@ccird3.UUCP (Rick Inzero) writes: >I may have missed a follow-up where my question was answered, but: >just what's so technologically difficult here, regarding the UV LEDs? Finding a wide, direct bandgap semiconductor that can be doped n and p type. Making it pure enough that midgap states won't overwhelm band-to-band recombination (which gets exponentially tougher as the bandgap increases). Making ohmic contact to it. Hoping that it has mechanical and thermal properties that allow it to tolerate operating conditions. Finding a market for it that justifies the R&D expense. Among others... -- John Berryhill 143 King William, Newark DE 19711
greg@bluemtn.uucp (Greg Richter (2XS)) (07/19/90)
In article <1990Jul18.033929.13442@zoo.toronto.edu> henry@zoo.toronto.edu (Henry Spencer) writes: >In article <38692@cci632.UUCP> rdi@ccird3.UUCP (Rick Inzero) writes: >>Unless there's some problem with actually generating the UV from the >>light emitting diode chip itself... So far, all I remember is postings >>that the plastic housing was the problem. > and gets the response: >... The mechanisms and materials that fairly easily yielded IR, >red, yellow, and green simply can't be stretched to blue, let alone >further. ... Actually, the emitters are silicon carbide, and are quite the bitch to bond to. We are working with this nasty material, so this is not idle speculation. The problem with blue is not the material or the mechanism, it's actually putting it in a usable industrial form. Making them small is even tougher. You get what is known as 'dark line cracks' where the substrate cracks under the thermal stress of the lead weld. Makes dark lines appear in the LED. Pleasantly - -GR -- "Nothing to say, no place to say it." | Greg Richter | ..{uunet,emory}!bluemtn!greg -------------------------------------------------------------------------
strong@tc.fluke.COM (Norm Strong) (07/19/90)
In article <1990Jul18.033929.13442@zoo.toronto.edu> henry@zoo.toronto.edu (Henry Spencer) writes: }In article <38692@cci632.UUCP> rdi@ccird3.UUCP (Rick Inzero) writes: }>Unless there's some problem with actually generating the UV from the }>light emitting diode chip itself... So far, all I remember is postings }>that the plastic housing was the problem. } }That's a side issue; the hard part is getting short-wavelength emissions }out of semiconductors at all. (Nondestructively, that is! :-)) It's not }a packaging problem that has delayed useful blue LEDs until quite }recently. The mechanisms and materials that fairly easily yielded IR, }red, yellow, and green simply can't be stretched to blue, let alone }further. My impression is that the blue ones are a triumph over major }difficulties, and nobody's in a hurry to tackle UV. Yes, indeed. And I'll bet the RIAA is heaving a big sigh of relief. CDs already last too long in their opinion. They used to be able to sell an LP with Brahms' 4th. Now with CDs, they have to throw in at least the Tragic Overture in order to be competitive. Can you imagine the problems of a CD that would last 3 hours? That's about how long they'd last if the laser worked at 400nm. -- Norm Strong (strong@tc.fluke.com) 2528 31st S. Seattle WA 98144