This animation demonstrates the effect of changing the bandgap in a semiconductor. When the electrons have to go from the n-type layer to the p-type layer, they have to lose energy. And this energy is imparted as photons. That’s how the LED works.
Since the LED is now immersed in liquid nitrogen, the band gap ( the difference in energy between the n-type and p-type layers ) has increased. And therefore the energy of the light emitted is also increased. Orange( Lower energy ) – > Green ( Higher Energy )
Video source:https://www.youtube.com/watch?v=GJyHdS8UouY
Bangap - read & learnhttp://news.mit.edu/2010/explained-bandgap-0723
Reference:http://www.oberlin.edu/physics/catalog/demonstrations/em/LEDinLN2.html
Paper:http://pubs.acs.org/doi/abs/10.1021/ed069p151?journalCode=jceda8
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