Green emission ZnO quantum dots were synthesized by an ultrasonic microreactor. Ultrasonic radiation brought bubbles through ultrasonic cavitation. These bubbles built microreactor inside the microreactor. The photoluminescence properties of ZnO quantum dots synthesized with different flow rate, ultrasonic power and temperature were discussed. Flow rate, ultrasonic power and temperature would influence the type and quantity of defects in ZnO quantum dots. The sizes of ZnO quantum dots would be controlled by those conditions as well. Flow rate affected the reaction time. With the increasing of flow rate, the sizes of ZnO quantum dots decreased and the quantum yields first increased then decreased. Ultrasonic power changed the ultrasonic cavitation intensity, which affected the reaction energy and the separation of the solution. With the increasing of ultrasonic power, sizes of ZnO quantum dots first decreased then increased, while the quantum yields kept increasing. The effect of ultrasonic temperature on the photoluminescence properties of ZnO quantum dots was influenced by the flow rate. Different flow rate related to opposite changing trend. Moreover, the quantum yields of ZnO QDs synthesized by ultrasonic microreactor could reach 64.7%, which is higher than those synthesized only under ultrasonic radiation or only by microreactor.

Green emission ZnO quantum dots were synthesized by an ultrasonic sol-gel method. The ZnO quantum dots were synthesized in various ultrasonic temperature and time. Photoluminescence properties of these ZnO quantum dots were measured. Time-resolved photoluminescence decay spectra were also taken to discover the change of defects amount during the reaction. Both ultrasonic temperature and time could affect the type and amount of defects in ZnO quantum dots. Total defects of ZnO quantum dots decreased with the increasing of ultrasonic temperature and time. The dangling bonds defects disappeared faster than the optical defects. Types of optical defects first changed from oxygen interstitial defects to oxygen vacancy and zinc interstitial defects. Then transformed back to oxygen interstitial defects again. The sizes of ZnO quantum dots would be controlled by both ultrasonic temperature and time as well. That is, with the increasing of ultrasonic temperature and time, the sizes of ZnO quantum dots first decreased then increased. Moreover, concentrated raw materials solution brought larger sizes and more optical defects of ZnO quantum dots.

Zn[Cr_xGa_(1−x)]₂O₄ (abbreviated Cr-ZGO) ceramics with x = 0–0.15 were synthesized by the conventional solid state method. The correlation between the microwave dielectric properties and the changes in the crystal structure and cation distribution of Cr-ZGO as a function of Cr³⁺ substitution for Ga³⁺ has been systematically investigated. The addition of Cr³⁺ promotes the densification of the ceramics and results in a normal spinel structure with Cr³⁺ occupying an octahedral site. With an increase in the Cr³⁺ content from 0 to 15 mol%, the ε_r of the ceramics increases, while the τ_f remains almost unchanged and the Q × f values ramp up to a maximum at 1 mol% Cr³⁺ addition and then ramp down continuously. 1Cr-ZGO exhibits the best microwave dielectric properties, with ε_r, Q × f, tan δ and τ_f being 9.88 (@9.9 GHz), 111 470 GHz, 8.87, and −74 ppm °C⁻¹, respectively. The Q × f value was increased by almost 40% compared with the pure ZGO ceramics (∼80 000 GHz). The enhancement of ε_r and Q × f values of Cr-ZGO can be attributed to the better bulk density, but further analysis by Rietveld refinement, Raman spectroscopy and FT-IR spectroscopy elucidated that the octahedral tilting in the spinel structure and the degree of short-range cation distribution are other governing factors. The effect of Cr³⁺ substitution for Ga³⁺ on the octahedral distortion and cation distribution in the spinel structure has been discussed in detail.

The structures and band structures of Sn doped ZnO were investigated by density functional theory (DFT). Sn-doped ZnO quantum dots were also synthesized via an ultrasonic sol–gel method. The charge of Sn ions was also taken into consideration and Sn²⁺ and Sn⁴⁺ were employed. UV-Vis absorption spectra and photoluminescence excitation spectra were used to elucidate the band gap of Sn-doped ZnO QDs. Photoluminescence spectra were employed to study the change in the defects of Sn-doped ZnO QDs. Sn doping reduced the symmetry of the ZnO cell and stretched the cell. Furthermore, it also could change ZnO from a direct gap semiconductor to an indirect gap semiconductor. The experimental results and DFT calculations matched quite well. Both the DFT calculations and experimental results showed that with an increasing Sn content, the band gap of Sn-doped ZnO first decreased and then increased, whereas the band gap of the ZnO base only increased. Sn doping also changed the optical defects of the quantum dots from defects to O_Zn and O_i defects.