Currently, developments in the field of quantum dots (QDs) have attracted researchers worldwide. A large variety of QDs have been discovered in the few years, which have excellent optoelectronic, antibacterial, magnetic, and other properties. However, ZnO is the single known material that can exist in the quantum state and can hold all the above properties. There is a lot of work going on in this field and we will be shorthanded if we do not accommodate this treasure at one place. This manuscript will prove to be a milestone in this noble cause. Having a tremendous potential, there is a developing enthusiasm toward the application of ZnO QDs in diverse areas. Sol–gel method being the simplest is the widely-favored synthetic method. Synthesis via this method is largely affected by a number of factors such as the reaction temperature, duration of the reaction, type of solvent, pH of the solution, and the precipitating agent. Doping enhances the optical, magnetic, anti-bacterial, anti-microbial, and other properties of ZnO QDs. However, doping elements reside mostly on the surface of the QDs. The presence of doping elements inside the core is still a major challenge for doping techniques. In this review article, we have focused on pure, rare-earth, and transition metal-doped ZnO QD properties, and the various synthetic processes and applications. Quantum confinement effect is present in nearly every aspect of the QDs. The effect of quantum confinement has also been summarized in this manuscript. Furthermore, the doping of rare earth elements and transition metal, synthetic methods for different organic molecule-capped ZnO QDs, mechanisms for reactive oxygen species (ROS) generation, drug delivery system for cancer treatment, and many more application are discussed in this paper.

A new photoactive hybrid nanostructure formed through an integration of quantum dots (QDs) and metal organic frameworks (MOFs) has been explored and assessed for its photocatalytic and photovoltaic performance. To this end, the QD–MOF nanocomposite was synthesized by mixing CdTe QDs during the formation of a titanium-based MOF ‘NTU-9,’ with titanium isopropoxide as a metal source and 2,5-dihydroxyterephthalic acid (H₄DOBDC) as an organic ligand. The successful formation of this nanocomposite is verified using various microscopic and spectroscopic techniques. Because the CdTe/NTU-9 composite exhibited a considerably broadened light absorption profile, it has achieved a rapid (30 min) and visible light-driven photocatalytic degradation (>95%) of rhodamine 6G. Further, when this composite is tested as a photoanode material in a QD-sensitized solar cell (QD-DSSC), its power conversion efficiency improved by approximately 1.5% relative to the raw QD form. Accordingly, CdTe/NTU-9 is demonstrated as a potential candidate for future applications in photocatalysis and DSSCs. The key features of the proposed nanocomposite include improved light absorption, sub-micron scale processing, chemical and thermal stability, easier regeneration, and better photocatalytic/photovoltaic characteristics.