Rapid synthesis of stable ZnO quantum dots

Zinc oxide nanocrystallites down to 1.5 nm in diameter were made by spray combustion of Zn/Si precursors. These crystallites exhibit a quantum size effect: blueshift of light absorption with decreasing crystallite size. X-ray diffraction, high-resolution transmission electron microscopy, and nitrogen adsorption showed that the addition of controlled amounts of silica prevented the growth and stabilized the ZnO crystals. The blue shift of the ultraviolet-vis absorption edge with decreasing ZnO crystal size closely followed a correlation between optical band gap and crystallite size from the literature. The band-gap energy of these ZnO quantum dots increased with silica content in the spray and particles consistently. The as-prepared quantum dots were stable and did not require any post processing.