Low-temperature solvothermal synthesis of ZnO quantum dots

ZnO quantum dots were synthesized via a low-temperature solvothermal process without using surfactants. Heat treatment of ZnCl₂ and NaOH solutions in tetra-ethylene glycol at 140°C led to the formation of spherical ZnO nanoparticles consisting of the aggregates of uniform-sized quantum dots. The particle size and morphology were characterized using transmission electron microscopy, dynamic light scattering, X-ray diffraction, and Brunauer-Emmett-Teller gas absorption measurements. It was found that the quantum dots in the particles were single crystals of ZnO of ∼5 nm in diameter having the wurtzite structure. The quantum dots showed quantum size effects even in the agglomerated form. The growth mechanism of this new type of ZnO nanoparticles is proposed.