Blue-Emitting Colloidal In1-xGaxP Quantum Dots Synthesized in Molten Salt: Toward Blue QLEDs with Improved Stability

Colloidal quantum dots (QDs) are being actively explored for QD light-emitting diode (QD-LED) displays with high color purity and wide color gamut, high brightness, and low-cost, solution-based manufacturing. Heavy metal-free InP QDs have enabled red- and green-emitting QD LEDs with excellent device characteristics. However, the performance of blue QD-LEDs, required for completing the red, green, and blue (RGB) full color gamut, is lagging behind, which prompts searches for novel blue-emitting QDs. Here, we report the synthesis, computational modeling, and structural and spectroscopic studies of heavy metal-free blue-emitting core-shell QDs featuring 2.1 nm In1-xGaxP cores, colloidally synthesized in a molten inorganic salt, epitaxially coated with ZnS shells, and optimized surface treatments. The computational study suggests that the introduction of a ZnS shell induces mixing between core and shell electronic states, enhancing the direct-gap character of In1-xGaxP/ZnS QDs. The resulting In1-xGaxP/ZnS QDs show blue band-edge photo- and electroluminescence that can be fine-tuned around the technologically important region of 470 nm. This material holds strong promise for filling the blue gap in full-gamut QD-LED displays.