Different valence Sn doping - A simple way to detect oxygen concentration variation of ZnO quantum dots synthesized under ultrasonic irradiation.

An ultrasonic method is employed to synthesize the Sn doped Zn0.95 Sn0.05 O quantum dots with green light emission. Sn2+ and Sn4+ ions are used to create different optical defects inside Zn0.95 Sn0.05 O quantum dots and the changing trend of oxygen concentration under different ultrasonic irradiation power are investigated. The photoluminescence spectra are employed to characterize the optical defects of Zn0.95 Sn0.05 O quantum dots. The UV-vis spectra are used to study the band gap of Zn0.95 Sn0.05 O quantum dots, which is influenced by their sizes. The results indicate that ultrasonic power would influence the size of Zn0.95 Sn0.05 O quantum dots as well as the type and quantity of defects in ZnO quantum dots. Changing trends in size of Sn2+ and Sn4+ doped Zn0.95 Sn0.05 O quantum dots are quite similar with each other, while the changing trends in optical defects types and concentration of Sn2+ and Sn4+ doped Zn0.95 Sn0.05 O quantum dots are different. The difference of the optical defects concentration changing between Sn2+ doped Zn0.95 Sn0.05 O quantum dots (VO defects) and Sn4+ doped Zn0.95 Sn0.05 O quantum dots (OZn and Oi defects) shows that the formation process of ZnO under ultrasonic irradiation wiped oxygen out.