Novel InP-based quantum dots via ZnO shelling and ruthenium doping for lighting and antibacterial applications

Semiconductor colloidal quantum dots (QDs) have been at the focus of attention in recent years due to their advantageous properties, including emission tunability by quantum confinement effect and material composition, high photoluminescence quantum yield (PLQY), and chemical stability. Thus, QDs are regarded as ideal materials for a wide variety of applications such as light-emitting diodes (LEDs) and photocatalysis. In the first part of our thesis, we demonstrated highly efficient quasi-type-II InP/ZnO/ZnS core/shell QDs with a PLQY of 91%. It is generally accepted perspective that type-II core/shell QDs, in which electron and hole wavefunctions are spatially separated, exhibit low PLQY. Even though type-II QDs with high PLQY values have been reported recently, they consist of heavy metals which show toxic effects. In our study, we used environmentally benign InP-based QDs as an alternative material compared to cadmium counterparts. After the synthesis of InP core QDs, we grew ZnO shell by thermal decomposition process to obtain type-II heterostructure. Subsequently, multiple ZnS shells were grown by SILAR technique. We integrated as-synthesized core/shell QDs on blue LED die using a novel architecture in liquid-state to minimize the host material effect. The resulting QD-LED exhibited external quantum efficiency (EQE) of 9.4%. In the second part of thesis, we introduced for the first-time ruthenium doping into InP/ZnS QDs as alternative strategy for efficient red-emitters. To date, various transition metals doping into InP QDs have been investigated, however, ruthenium (Ru) ion doping into InP QDs has not been explored yet. In our study, we synthesized Ru doped InP QDs by hot injection of ruthenium precursor into main solution at elevated temperature. Ru presence was confirmed by optical and structural analysis techniques. Ru doped InP-based QDs displayed higher PLQY in the red spectral region compared to undoped sample. The integration of Ru-doped QDs into LEDs in a liquid matrix led to an external quantum efficiency of 7.9%. In the last part of thesis, we investigated the potential of InP/ZnO core/shell QDs with type-II band alignment as a novel antibacterial agent. To date, various types of colloidal QDs have been introduced for antibacterial applications, including InP, ZnO, and CdTe. However, antibacterial activity of the type-II based QDs have not been studied yet. In our study, we demonstrated that InP/ZnO QDs exhibited reactive oxygen species (ROS) generation, including superoxide (•O2⁻) and hydroxyl radicals (•OH). Furthermore, upon low intensity green light stimulation (3 mW.cm-2) the optimized core/shell QDs displayed high antibacterial activity of 99% inhibition against Pseudomonas aeruginosa. These findings showed novel InP-based QDs via ZnO shelling and ruthenium doping are efficient material for LED and antibacterial applications.