NOVELTY - Synthesizing (M1) monodisperse metal chalcogenides nanocrystals involves combining metal precursor, ligand, and chalcogenide precursor in a first non-coordinating solvent to form first composition of nanocrystal; reacting core nanocrystals with a metal composition of metal oxide with an additive composition of acid or amine and chalcogenide precursor in second non-cordinating solvent to form second composition; and adding phosphine-free metal precursor, ligand, and chalcogenide precursor to first and second compositions to obtain monodisperse core/multi-shell metal chalcogenide nanocrystal.    USE - For synthesizing monodisperse metal chalcogenides nanocrystals selected from alloyed, core-shell, and doped semiconductors for converting into water-soluble nanocrystal for biological labeling, imaging reagent, and manufacture of light-emitting diode, solid state lighting, and a solar cell device (claimed).    ADVANTAGE - The method is one-spot reaction method; is simple and high performance version of the industrial scale synthesis; prepares monodisperse metal chalcogenides nanocrystals without using air-sensitive alkylphosphine; and manufactures high quality monodisperse metal chalcogenides nanocrystals, with low cost.    DETAILED DESCRIPTION - Synthesizing (M1) monodisperse metal chalcogenides nanocrystals involves providing a first composition of nanocrystal by combining metal precursor, ligand, and chalcogenide precursor in a first non-coordinating solvent at a first preset reaction temperature, where the metal precursor can be dissolved in the ligand and the first non-coordinating solvent and the first preset reaction temperature is sufficient for forming the first composition of nanocrystal in dot-shape, rod shape, branch shape and wire shape to obtain a final product of highly monodisperse metal chalcogenide nanocrystals; providing a core/shell nanocrystals-synthesis, which provides a second composition through a second reaction by pre-selected core nanocrystals reacting with a metal composition consisting of metal oxide or salts with an additive composition consisting of acid or amine and chalcogenide precursor in a second non-cordinating solvent at a second preset temperature of 100-350 degrees C for a second preset period of time of 5 minutes to 10 days to obtain a final product of highly monodisperse core/shell metal chalcogenide nanocrystals; and adding at least one phosphine-free metal precursor, ligand, and chalcogenide precursor to the first and the second compositions to obtain a final product of highly monodisperse core/multi-shell metal chalcogenide nanocrystals. An INDEPENDENT CLAIM is included for preparing (M2) water-soluble nanocrystal from organic solvent-soluble nanocrystal, adapted for applying in industrial manufacture, involving preparing a solution A by dissolving the organic solvent-soluble purified nanocrystals in organic solvent; preparing a solution B by dissolving an amphiphilic oligomer in distilled water and adjusting the pH of solution B to 8-10; and mixing the solution A and solution B (VB greater than VA) to form an emulsion system under magnetic stirring; and evaporating the organic solvent from the mixed solution at room temperate to obtain the water soluble nanocrystals or photoluminescent microspheres, where the molar ratio of nanocrystal/PMAA is 1:10-1:200 and the volume ratios of water/organic solvent is 3:1-9:1, where the water soluble nanocrystals or photoluminescent microspheres are capable of being applied at industrial level for biological labeling, imaging reagent, and manufacture of light-emitting diode, solid state lighting, and a solar cell device.