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0 pointsPaulHoule1y ago0 comments

This reminds me of the observation I had in high school that I could immerse LEDs in liquid nitrogen and run them at higher than usual voltage and watch the color change.

I got a PhD in condensed matter physics later on but never got a really good understanding of the phenomenon but I think it has something to do with

https://www.digikey.com/en/articles/identifying-the-causes-o...

Here is a video of people doing it

https://www.youtube.com/watch?v=5PquJdIK_z8

0 comments

duskwuff1y ago

> I got a PhD in condensed matter physics later on but never got a really good understanding of the phenomenon but I think it has something to do with

The color of most* LEDs is controlled by the band gap of the semiconductor they're using. Reducing the temperature of the material widens the band gap, so the forward voltage of the diode increases and the wavelength of the emitted light gets shorter

https://www.sciencedirect.com/science/article/abs/pii/003189...

*: With the exception of phosphor-converted LEDs, which are uncommon.

exmadscientist1y ago

> phosphor-converted LEDs, which are uncommon

No, they're extremely common. Every white LED in the market is phosphor-converted: they're blue LEDs, usually ~450nm royal blue, with yellow-emitting phosphors on top. Different phosphors and concentrations give different color temperatures for the final LED, from about 7500K through 2000K. (Last I looked, anything below about 2000K didn't look right at all, no matter what its manufacturer claimed.)

Bigger LEDs are often phosphor-converted as well. Most industrial grow lamps use this type of LED. So they're around! You're probably looking at some right now!

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