In this study, monodispersed CdSe nanocrystal (NCs) were prepared by means of solution-phase synthesis. CdSe/CdS NCs were synthesized via successive ion layer adsorption and reaction on CdSe core NCs. The optical properties of CdSe and CdSe/CdS core/shell NCs dissolved in different solvents were investigated. We discuss here the photoluminescence properties of an NC system that are affected by the NC concentration and the solvent variety, including photoluminescence intensity variation and photoluminescence peak shift. The change in emission intensity is due to the influence of the solvent polarity and the NC concentration quenching effect. The phenomenon of a large blue shift of photoluminescence peaks with NC concentration is caused by interactions among the NCs.