A diamond diode can produce single photons at room temperature in response to a small electrical current.

Devices that can produce one photon at a time have potential applications in quantum communication and computation, but usually require very low temperatures. Norikazu Mizuochi at Osaka University in Japan and his colleagues say that the key feature of their diode is a diamond layer that contains gaps in the carbon lattice occupied by nitrogen atoms. The researchers theorize that these nitrogen-vacancy complexes naturally capture positively charged 'holes' and electrons from a small electrical current that recombine and emit light.

Nature Photon. http://dx.doi.org/10.1038/nphoton.2012.75 (2012)