When you drop lasers and LEDs into liquid nitrogen, the lights cool down and start turning one color into another. In the GIF above you’ll see it start from a urine yellow to a Mountain Dew color and then to a radiator fluid green and finally some super alien blood goo substance. It’s great!
This experiment works by utilizing liquid nitrogen to cool the semiconductor to -196ºC, robbing it of much of its thermal energy. This causes the “bandgap” energy to increase, thereby increasing the emitted photon energy and decreasing the emission wavelength.