a coated nanocrystal capable of light emission includes a substantially monodisperse nanoparticle selected from the group consisting of cdx , where x = s , se , te and an overcoating of zny , where y = s , se , uniformly deposited thereon , said coated nanoparticle characterized in that when irradiated the particles exhibit photoluminescence in a narrow spectral range of no greater than about 60 nm , and most preferably 40 nm , at full width half max . the particle size of the nanocrystallite core is in the range of about 20 å to about 125 å , with a deviation of less than 10 % in the core . the coated nanocrystal exhibits photoluminescence having quantum yields of greater than 30 %.