Effect of reaction temperature and reaction time on the sizes and defects of Sn doped ZnO quantum dots synthesized under ultrasonic irradiation

Sn doped Zn_0.95Sn_0.05O quantum dots were synthesized via an ultrasonic method under different reaction time and reaction temperature. Optical defects of these Zn_0.95Sn_0.05O quantum dots were controlled by tuning the valence states of the dopants (Sn²⁺ or Sn⁴⁺). For Sn²⁺ doped Zn_0.95Sn_0.05O quantum dots, main optical defects were VO· defects. While for Sn⁴⁺ doped Zn_0.95Sn_0.05O quantum dots, main optical defects were O_{Z n} and O_i defects. UV–Vis spectra were employed to investigate the energy gap of these quantum dots. Photoluminescence properties were measured to discuss the optical defect types and concentrations in these quantum dots. It was found that the reaction condition played an important role in controlling the particle sizes and optical defects of Zn_0.95Sn_0.05O quantum dots. Moreover, with reaction temperature or reaction time increasing, for both Sn²⁺ and Sn⁴⁺ doped Zn_0.95Sn_0.05O quantum dots, changing trends of their particle sizes were almost same. While changing trends of their optical defect types and concentrations were different. The results indicate that, oxygen in Sn doped Zn_0.95Sn_0.05O quantum dots died out much more completely under the ultrasonic reaction with higher reaction temperature and longer reaction time.