Highly Stable Core/Shell AgIn5S8/ZnS Quantum Dots for Pure White Light-Emitting Diodes

AgIn 5 S 8 /ZnS (AIS/ZS) core/shell quantum dots (QDs) have been synthesized using a hot injection method at relatively low temperature without any protection using inert gas. The QDs were characterized with UV visible electronic absorption spectroscopy, PL spectroscopy, Fourier transform infrared (FT-IR) spectroscopy, transmission electron microscopy (TEM), and temperature-dependent time-resolved PL (TRPL). The average size of the QDs was determined to be 1.73 ± 0.29 nm. The QDs exhibit a major excitonic absorption band peaked at 479–573 nm and emission bands peaked from 548 to 666 nm with excitation at 410 nm with the peak position dependent on the synthesis temperature that affects the QD size. Upon the addition of trioctylphosphine (TOP) as a ligand, the PL quantum yield (PLQY) increased to 74.1% compared to 56.7% without TOP. The QDs show high stability after hours of ultraviolet (UV) light exposure or repetitive treatment with a significant amount of polar solvents, which is attributed to surface passivation by the ligands and ZnS shell. The luminescence mechanism of the core/shell AIS/ZS QDs is ascribed to donor–acceptor pair (DAP) recombination. TRPL results suggest that the binding energy of DAP increases and the DAP recombination probability is enhanced after passivation with TOP, leading to the high PLQY. Furthermore, prototype highly pure white light-emitting diodes (LEDs) based on these AIS/ZS QDs have been successfully demonstrated, yielding ideal 1931 CIE coordinates of (0.327, 0.335).