MgO gets discrete: Monodisperse nanocrystals of the alkaline earth metal oxide MgO can be prepared by direct colloidal synthesis (see image). Diameter control (2-8 nm) is achieved by incorporating catalytic amounts of water into the organic reaction medium. Although trioctylphosphine oxide is present during the reaction, the resulting nanocrystals are capped primaryly by benzyl ether. Blue luminescence is observed with a quantum yield up to approximately 20 %.