PROBLEM TO BE SOLVED: To provide a semiconductor device nanocrystal exhibiting a high quantum yield with photoluminescence emission of a high spectrum purity. SOLUTION: A coated nanocrystal capable of light emission includes a core that is a part of a set of substantially monodisperse nanoparticles selected from the group consisting of CdX, wherein X represents S, Se, Te, and mixtures thereof; and an overcoating of ZnY, wherein Y represents S, Se, uniformly deposited thereon, the coated core is coated nanocrystals which exhibit photoluminescence in a narrow spectral range of no greater than about 60 nm, and most preferably no greater than 40 nm, at full width half max (FWHM) when the core is irradiated. The particle size of the core is in the range of about 2 nm (20 Å) to about 12.5 nm (125 Å), with a deviation of less than 10% in the core. COPYRIGHT: (C)2010,JPO&INPIT