We have studied synthesis, properties, and formation mechanism of II-VI semiconductor nanoparticles (NPs) such as CdO, CdSe and CdTe. The first part describes the synthesis, structure and the optical properties of 3-5 nm CdO/Cd(OH)₂/CdCO₃ NPs synthesized by the reaction between CdO and 2-[2-(2-methoxyethoxy)ethoxy]acetic acid. The NPs show unusual fluorescence at 450 nm. The second part contains detailed solution NMR study of the reaction mechanism and surface structure of CdO/Cd(OH)₂/CdCO₃, CdSe, and CdTe NPs. Formation of CdO/Cd(OH)₂/CdCO₃ NPs was monitored by ¹H and ¹³C NMR. Increasing NMR line-broadening is attributed to NPs core formation. Reactions of trioctylphosphine (TOP) chalcogenides (TOPE; E=Se, Te) and cadmium nonanoate (Cd(NA)₂) were monitored in hexane at 47-60 °C by ¹H, ³¹P NMR and optical spectroscopy. ¹³C, ³¹P and ¹¹³Cd NMR were used to investigate of the mechanism of formation of ultrasmall CdSe and CdTe NPs. Cd(nonanoate)₂-TOP complex was found to be the Cd precursor in this reaction. Slow exchange of TOP with TOPSe ultimately produced CdSe NPs. Trioctylphosphine oxide (TOPO) and nonanoic anhydride were identified as byproducts of this reaction. TOP, TOPO, TOPSe, and nonanoate were all found to be surface ligands for CdSe NPs.