Highly monodisperse zinc blende CdSe nanocrystals have been synthesized by using different phosphine-free Se precursors successfully. To understand the reaction mechanism and obtain high quality CdSe nanocrystals, the effects on the use of different Se and/or Cd precursors, the adjustment of the molar ratios between Cd and Se precursors, and the selection of suitable reaction and growth temperatures have been studied in details. Absorption spectrum, fluorescence spectrum, X-ray diffraction (XRD), and transmission electron microscopy (TEM) were used for the characterization of synthesized CdSe nanocrystals. The quality of as-prepared CdSe nanocrystals was reached the same high level compared with the method using phosphine selenium precursors, its quantum yields were among 30 to 60% and photoluminescence (PL) full width at half-maximum (FWHM) was well controlled between 22 and 28 nm. As core, such zinc blende CdSe nanocrystals were also used to synthesize CdSe/ZnS, CdSe/CdS, and CdSe/CdS/ZnS core-shell nanocrystals. The quantum yields of as-prepared core-shell nanocrystals were among 50 to 80%. Large-scale syntheses of such core-shell nanocrystals have been successfully demonstrated and as many as 3 g of high quality CdSe/ZnS nanocrystals were easily synthesized with the use of only low-cost, green, and environmentally friendlier reagents.