Optical gain and lasing in a semiconductor embedded in a three-dimensional photonic crystal

Three-dimensional photonic crystals used in this study were synthetic opals, composed of submicron silica spheres, close-packed in a face-centered cubic structure with a period of 200 nm, which exhibit photonic stop-bands around 600 nm. We report on a substantial optical gain in CdS nanocrystals embedded inside the interstitials between the silica spheres. It is found that the optical gain is enhanced at the edges of the photonic gap due to multiple coherent Bragg scattering of light in the periodic photonic crystal. The latter provides an efficient feedback mechanism for lasing action.