Realization of InP/ZnS quantum dots for green, amber and red down-converted LEDs and their color-tunable, four-package white LEDs

Abstract

Eco-friendly InP/ZnS quantum dots (QDs) have been synthesized by the conventional hot injection method using a non-toxic and economic P(N(CH₃)₂)₃ precursor. The carefully controlled synthesis of a series of InP/ZnS QDs was performed by varying the core-growth temperature and time, the [P]/[In] ratio, and the number of ZnS shell coatings. The full-width at half maximum (FWHM) of the photoluminescence (PL) emission peaks from orange-red InP/ZnS QDs can be reduced from 73 to 56 nm by increasing the [P]/[In] ratio from 1.5 to 3.0. This is because there is concurrent formation of InP nuclei during the step in which excess volatile P-precursor is injected. The triple-shell-coated InP/ZnS core–shell QDs of green (G), yellow (Y), and orange-red (OR) colors reached PL quantum yields as high as 0.50, 0.63, and 0.55; and FWHMs of PL peaks as narrow as 55, 76, and 71 nm, respectively. This is the first realization of a variety of efficient green, amber (A), and red (R) monochromatic, down-converted, light-emitting diodes (DC-LEDs) using InP/ZnS QDs. They are fabricated by simply capping a long-wave pass dichroic filter (LPDF) on top of the LED packing associated with each corresponding InP/ZnS QD. In this study, we also characterized the vision and color performance using luminous efficacy, color-rendering index (CRI), special CRI for a strong red (R₉) and color quality scale of color-tunable, four-package white LEDs. These consisted of InP/ZnS QD-based G, A, and R monochromatic, LPDF-capped DC-LEDs and a blue InGaN LED. The good optical performance of the InP/ZnS QD-based monochromatic DC-LEDs and their four-package white LEDs could provide the possibility of applying environmentally clean InP/ZnS QDs in monochromatic LEDs in the wavelength ranges of the “green gap”; thereby creating high-quality-color, color-tunable, four-package white LEDs.