Would you look at that. Green light. Out of the unlikely material of silicon. Those good researchers are intent on making silicon the go-to material for integrated photonics -- or integrated optics -- or photonic integrated circuits (PICs) -- or photonic lightwave circuits (PLCs) -- or whatever term suits your fancy.

The photonic crystal--the slab of material with holes in it--is able to sufficiently slow the propagation of light which, in turn, strongly interacts with that holey material. During this interaction, green light is produced.