Near-Unity Photoluminescence Quantum Yield of Green-Emitting Graded-Alloy Core/Shell Giant Quantum Dots by z-Type Ligand Passivation for Display Applications

As-synthesized, green-emitting graded-alloy core/shell “giant” quantum dots have outstanding properties that can be utilized for different optoelectronic applications. But often, defects arise upon nonuniform growth of the shell. These surface defects affect the photoluminescence quantum yield (PLQY), lifetime, and stability of the green-emitting graded-alloy core/shell “giant” quantum dots. So, to overcome these surface traps, the graded-alloy core/shell g-QDs were passivated with z-type ligands (ZnCl2, CdCl2, and MgCl2). The change in the PLQY, lifetime, and photoluminescence emission confirmed that the z-type ligands are passivating the trap states of g-QDs by bonding with an unsaturated chalcogenide atom on the surface, and this was confirmed by X-ray photoelectron spectroscopy. All three cases (treated with ZnCl2, CdCl2, and MgCl2) showed outstanding enhancement in the photoluminescence quantum yield. Fascinatingly, the ZnCl2-treated g-QDs showed maximum enhancement in the PLQY from 62% to unity. Furthermore, the photostability test was performed under continuous UV-light irradiation for 24 h, which clearly showed superior photostability. Moreover, the temperature-dependent stability of untreated and treated g-QDs was studied from 10 to 90 °C. Furthermore, the green-emitting down-converted LED was fabricated by utilizing ZnCl2-treated g-QDs, which show great potential for display application.