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I've been working on an experiment where I dip LEDs into liquid nitrogen and note the color change. All online sources I've seen predict that the wavelength of the light emitted by the LED will decrease upon immersion. What I've been observing, however, is a sudden decrease in wavelength followed by a definite increase in wavelength. So, for example, a yellow LED turned green-ish at first, and then rapidly changed to yellow-orange.

I've been looking around for an explanation of why I am getting this (opposite) effect, but haven't had any luck. Does anyone have any ideas?"

Quoted from Re: Increase in Wavelength of an LED Immersed in Liquid Nitrogen

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Hmm, this is a bit strange. I have noticed the shift to shorter wavelengths several times with different LEDs but never the opposite. In a simple theoretical picture this should not happen. The second change cannot be associated with the temperature alone, something else must change the physical properties. – Alexander Oct 25 '12 at 11:00
As far as I know, the yellow and green LEDs are not based on pure semiconductors like the red and blue ones are. Notice also we are not able to make competitive led or yellow diode lasers. Thus there may be many mechanisms of light emission at impurities that shift in frequency or change their efficiency, or both, when the temperature drops. – dominecf Mar 1 at 15:08

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