led's

Dear All,

just curiosity, maybe it seems stuped but I want to know something
about led's.How much energy does an led emit and what determines the
color of the light?

Thanks in advance

ps if you know any sites where I can find more information about
led's, let me know!

Lynn

 

That depends on the LED.

I think it's the bandgap that determines the wavelength - and thats affected
by the materials and dopants used. You can get visible ones, infra-red,
ultra-violet, laser...

There must be loads of websites out there...

Ben

 

I'm not sure about energy or know of websites describing them, but the color
is defined by the bandgap (distance between the valence and conduction
bands) of the semiconductor which it was made out of. Semiconductors which
have a large bandgap, like Indium-Gallium-Nitride (InGaN) impart more energy
into the photon and therefore emit blue or violet photons. Gallium-Arsenide
(GaAs) LEDs, having a smaller bandgap, are on the other side of the visible
spectrum emitting red or infrared light. Wide spectrum LEDs, like white
colored ones are actually a combination or red, green, and blue LEDs packed
closely togethor, or, I believe much more commonly, an InGaN LED coated with
phosphors.

In case if you're also curious, Silicon makes aboslutely lousy LEDs, even
though it is significantly cheaper semiconductor to manufacture. Almost all
of the energy you put into it gets wasted heating up the crystal lattice. I
might be wrong, but if I remeber correctly, the photons which do get emitted
are blue.

Howard Henry Schlunder

in message
news:...

 

Yeah, thats why they're rarely used for optical applications, despite the
cost consideration.

Thats possible, although true blue LEDs are a relatively new thing.

Ben

 

Ultra-violet LEDs? Where?

 

Well, a good place to start is The Led Museum:
http://www.ledmuseum.org )

And of course Don Klipstein's Web Site:
http://www.misty.com/people/don/index.html


Søren A.Møller

 

BivarOpto make them:

http://www.bivar.com/default.asp?p=products&c=UV LEDs

Toyoda Gosei make some too, can't find them on their website though.

RS do them:

Metal Can: E1L5M-3P0A2 and E1L5M-4P0A2
SMD: E1S19-0P0A7

Ben

 

The shortest wavelength LED using your link is 395nm. This would be classed
as violet rather than ultraviolet. The visible range is normally taken to
be nominally 400nm to 700nm.

 

The SMD ones are 374-401nm
Metal can are: 374-392nm

Here's one at 350nm:
http://www.roithner-laser.com/All_Datasheets/LEDs/RLT350-30.pdf

Which I think can be classed as NUV if nothing else.

Ben

 

Is there anything in the near future at near 250nm (germicidal?).

 

IIRC,All Electronics was selling 12 mW UV leds for a couple of bucks each
awhile back,not a bad price.
Or was it ALLtronics? AAACK!

 

www.ledmuseum.org and go to the links, www.nichia.com sells them, etc.,
etc., etc.,...



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Perhaps you are thinking of silicon carbide blue LEDs. Back in 1907 it was
discovered that silicon carbide could be made to electroluminesce. The
sample used back then probably contained some built in pn junctions.
Silicon carbide LEDs tend to have hideously bad luminous efficacy,
especially the ones that were briefly available around the early 1970's.
Silicon carbide is a wide bandgap semiconductor. Dim but practical blue
LEDs have been available with output peak wavelength of around 470nm. They
have since been greatly superceded by GaN blue LED technology.

Plain silicon does indeed make for terrible LEDs. Although the energy
bandgap is theoretically compatible with LED light production, silicon is
known as an "indirect semiconductor." One of the consequences of being an
indirect semiconductor is hole electron recombination doesn't normally
produce photons of your anticipated wavelength, but instead produces phonons
(as compared to photons) which are quanta of sound pressure waves, or in
other words lattice vibrations which is heat. Silicon doesn't produce any
particularly meaningful number of photons of any wavelength practical for
LED technology (at least until you start cranking the serious juice through
them and they start producing light just like any good blackbody radiator
should... but you aren't supposed to do that...).