Low-temperature organometallic nucleation and crystallization-based synthesis methods for the fabrication of semiconductor and metal colloidal nanocrystals with narrow size distributions and tunable, size- and shape-dependent electronic and optical properties. Methods include (1) forming a reaction mixture in a reaction vessel under an inert atmosphere that includes at least one solvent, a cationic precursor, an anionic precursor, and at least a first surface stabilizing ligand while stirring at a temperature in a range from about 50° C. to about 130° C. and (2) growing nanocrystals in the reaction mixture for a period of time while maintaining the temperature, the stirring, and the inert-gas atmosphere.