Bright Red-color Luminescence from Ag−In−Ga−S-based Quantum Dots with the introduction of Copper

This study presents cadmium-free, red-emission quantum dots (QDs) synthesized by incorporating Cu into silver indium gallium sulfide/gallium sulfide (Ag–In–Ga–S/Ga–S) core/shell QDs. By using a previous technique, in which the original Ag–In–Ga–S/Ga–S core/shell QDs exhibiting band-edge photoluminescence (PL) were improved to achieve a narrower emission and facile synthesis, we injected a mixture of Cu and Ag sources into a heated solution containing In, Ga, and S sources. This resulted in the formation of Ag–Cu–In–Ga–S quinary QDs without any precipitation. After being coated with a Ga–S shell, these QDs exhibit a red-colored PL with a spectral full-width at half maximum of 55–60 nm. Although the PL wavelength was responsive to changes in In/Ga ratios, it was unaffected by variations in Cu/Ag ratios due to the transition between conduction band electrons and holes localized at Cu cites. Notably, the electroluminescence device exhibited high-purity red light that satisfies the recommendation ITU-R BT.2020 standard. Cadmium-free Ag–Cu–In–Ga–S/Ga–S core/shell quantum dots were synthesized by a scalable method and red emission was obtained from a free-to-bound transition via Cu-related localized states. The emission wavelength was controlled by the In/Ga ratio, which allowed the fabrication of high-purity red electroluminescence in compliance with the ITU-R BT.2020 standard.