Low-temperature synthesis and characterization of ZnO quantum dots

ZnO quantum dots (QDs) were fabricated at low temperature of 200 °C through thermal decomposition method with slight introduction of sodium dodecyl sulfate (SDS). The morphology, structure and optical properties were investigated by the methods of X-ray diffraction (XRD), transmission electron microscope (TEM), photoluminescence (PL) and Raman spectrum, respectively. The XRD results showed the as-synthesized ZnO QDs had hexagonal wurtzite structure and the average grain size estimated from Scherrer formula was 7.5 nm which had a good agreement with TEM result. And it is evident that the introduction of SDS can actually decrease the grain size to form ZnO QDs. The Raman results also indicated that the ZnO QDs keep the overall crystal structure of the bulk ZnO. Both spatial confinement within the dot boundaries and phonon localization by defects were the mainly reason for the only few cm−1 redshift of the Raman scatter peaks. The room-temperature photoluminescence reveals that the as-prepared ZnO QDs exhibit an ultraviolet emission at 380 nm and a broad deep level emission band in the range of 420–700 nm in wavelength, which testified the Raman and XRD results that the as-synthesized ZnO QDs had defects. Moreover, the growth mechanism of ZnO QDs was also discussed in the article.