Monodispersed Spherical Colloids of Se@CdSe: Synthesis and Use as Building Blocks in Fabricating Photonic Crystals

Monodispersed spherical core−shell colloids of Se@Ag2Se have been exploited as a chemical template to synthesize Se@CdSe core−shell particles using a cation-exchange reaction. A small amount of tributylphosphine could facilitate the replacement of Ag+ by Cd2+ in methanol at 50 °C to complete the conversion within 150 min. The orthorhombic structure of β-Ag2Se changed to a well-defined wurtzite lattice for CdSe. The CdSe shells could be converted back to β-Ag2Se by reacting with AgNO3 in methanol at room temperature. Because of the uniformity in size and high refractive index associated with the Se@CdSe core−shell colloids, they could serve as a new class of building blocks to fabricate photonic crystals with wide and strong stop bands.