White light-emitting diodes based on quaternary Ag–In-Ga-S quantum dots and their influences on melatonin suppression index

Abstract

Light sources have effect on the circadian rhythms so as to the health of human. Therefore, both visual and non-visual effects should be considered when designing and fabricating light sources. Quantum dot (QD) materials have been extensively used as color converters to fabricate white light-emitting diodes (LEDs). However, most of the work on the photoluminescent QD-based LEDs (QLEDs) are focused on the improvement of visual performances. Here, quaternary Ag–In-Ga-S (AIGS)/ZnS QDs are synthesized for the application of white QLEDs taking both visual and non-visual performances into consideration. Theoretical calculation is carried out and the results show that QLEDs based on the combination of red emission QDs and green emission ones can exhibit a high color rendering index (CRI) of 90.8 and a color correlated temperature (CCT) of 5669 K, a melatonin suppression index (MSI) of 0.788. Furthermore, the combination of red 670 nm emission and green 550 nm AIGS/ZnS QDs are integrated with a blue-emission chip to fabricate QLEDs. The as fabricated devices exhibit a maximum CRI of 90.33, a CCT of 5947 K and an MSI of 0.7866, which are all consistent with the simulation results. These experimental results are comparable to those of some commercial white light sources. We discuss non-visual effects of QLEDs for the first time, and our research results show that AIGS/ZnS QDs, which are free-of heavy metal elements and have wide full-width of half maximums (FWHMs), are suitable for the fabrication white light sources with highly visual performances and tunable MSI values, which have many potential applications in the field of healthy lighting and environmentally friendly light sources.